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THE  EYES  OF 
THE  ARMY  AND   NAVY 

Practical  Aviation 

BV 

Albert  h.  munday 

FLIGHT  UEUTENANT,   R.  N. 

ILLUSTRATED 


HARPER    y    BROTHERS    PUBLISHERS 

NEW    YORK    AND     LONDON 


The  Eyes  of  the  Army  and  Navy 


Copyright,    1917,   by   Harper  &    Brothers 

Printed  in  the  United  States  of  America 

Published  October,  191 7 


CONTENTS 

PAGE 

Foreword xi 

Chapter  I.    Aerial  Navigation i 

Importance  of  Aerial  Navigation — The  Compass — Varia- 
tion— Deviation — To  Lay  Off  a  Course  by  Compass — 
The  True  Course  and  True  Bearing— The  Magnetic 
Course  and  the  Magnetic  Bearing — The  Compass  Course 
and  the  Compass  Bearing — To  Lay  Off  a  Course  Allowing 
for  Drift — To  Ascertain  a  Position  of  an  Aeroplane — Con- 
sideration of  Wind — Veering  of  the  Wind — Increase  in 
Velocity  of  Wind  as  Height  Is  Attained — Beaufort  Wind 
Scale — How  to  Ascertain  the  "Radius  of  Action"  of  an 
Aeroplane — "Radius  of  Action"  Returning  to  Different 
Position — "Radius  of  Action"  Returning  to  a  Seaplane 
Carrier — To  Intercept  an  Enemy  Machine. 

Chapter  II.    Theory  of  Flight 23 

Pressure — The  Action  of  Pressure  on  a  Flat  Plate — Lift 
Over  Drift  Ratio — Aspect  Ratio^ — Center  of  Pressure — 
The  Advantages  of  Curved  and  Flat  Planes — Stream-line 
Efifect — The  Dynamics  of  an  A  roplane — Lift  and  Drift 
on  a  Wing  Section  in  Motion — Loading — Weight,  Lift — 
The  Gliding  Angle — How  to  Ascertain  Visibility  of  Hori- 
zon— Miscellaneous  Formulae — Lift  and  Drift  Co-efi&cient, 
and  Aerodynamical  Efficiency  Curves. 

Chapter  III.    Map-reading 37 

The  Scale  of  a  Map — Definitions:  Basin,  Crest,  Contour, 
Dune,  Escarpment,  Gorge,  Hachures,  Knoll,  Meridian  or 
North  Line,  Magnetic  Meridian,  Pass,  Plateau,  Plotting, 
Salient  or  Spur,  Setting  or  Orienting  a  Map,  Under- 
feature.  Undulating  Ground,  Watercourse,  Watershed — 
Conventional  Signs  Adopted. 


CONTENTS 

PAGE 

Chapter  IV.    Cross-country  Flying 43 

Importance  of  Knowledge — General  Hints. 

Chapter  V.    Charts 51 

Starboard-hand  Buoys  —  Port-hand  Buoys  —  Middle- 
ground  Buoys — Telegraph  Buoys — Spoilt-ground  Buoys — 
Abbreviations — Lights. 

Chapter  VI.    Meteorology 57 

Importance  of  Knowledge — Aeroplane  Weather — Atmos- 
phere— Composition  of  Atmosphere — Atmospheric  Press- 
ure—Measure of  Pressure — Approximate  Relation  between 
Inches  and  Millibars  of  Pressure — High  and  Low  Pressure 
Regions — Cyclone  or  Low-pressure  Area — Line  Squalls — 
Anticylone — ^Wind — Beaufort  Scale — Veering  of  Wind 
— Increase  of  Velocity  of  Wind  Relative  to  Height — The 
Gradient  Wind — ^Wind  Eddies — Upward  Currents — De- 
scending Currents — ^Wind  Lay ers— Clouds :  The  Upper 
Layer,  The  Middle  Layer,  Heap  Clouds — Airship  and 
Balloon  Weather — Buys  Ballot's  Law — Conversion  of 
Temperature — Change  of  Temperature  Relative  to 
Height. 

Chapter  VII.    Construction 78 

Materials:  Ash,  Spruce,  Hickory,  Canadian  Elm,  Bass- 
wood,  Walnut,  Mahogany,  Three-ply  Wood — Metals: 
Aluminium,  Duralumin,  Manganese,  Phosphor-bronze, 
Steel — Fabric:  Securing  and  Repairing  Fabric;  To  Repair 
a  Tear  in  the  Fabric  when  Away  from  an  Aerodrome; 
Repairing  a  Tear  in  the  Fabric  at  an  Aerodrome — Dope : 
Its  Uses--Wires:  Flexible  Cable,  Attaching  Flexible 
Cable,  Solid-drawn  Wire,  Method  of  Attaching  Solid-drawn 
Wire,  Strength  of  Wire  and  Flexible  Cable,  Construction 
of  Principal  Parts  of  an  Aeroplane — Wings:  Ribs,  Struts, 
Attachment  of  Struts,  Wiring,  Flying- wires,  Landing-wires, 
Drift  Wires,  Incidence  Wires,  Method  of  Attaching  Wire 
— The  Body:  Fuselage  and  Nacelle  Covering — The  Tail: 
The  Landing-chassis,  or  Undercarriage;  The  Control  of 
a  Machine,  Control  Wires,  Lateral  Control,  Truing-up 
an  Aeroplane. 


CONTENTS 

PAGE 

Chapter  VIII.    The    Care    and   Maintenance   of   Aero- 
planes     104 

Importance — The  Handling  and  Transport  of  a  Machine — 
Filling  up  Machines — Priming  or  "Doping"  an  Engine — 
Preparations  for  Swinging  the  Propeller — Swinging  the 
Propeller — Cleaning  the  Machine — Storage  of  Aeroplane 
— Care  of  Material:  Fabric,  Wood,  Propellers,  Bracing 
Wires,  Tires,  Field  Repairs. 

Chapter  IX.    Aero  Engines 116 

Requirements — Rotary  Engines — Stationary  Engines,  Air- 
cooled  and  Water-cooled — Magnetos:  Action  of  the 
Magneto,  Platinum  Points  of  Magnetos,  High-tension 
Terminal,  Low-tension  Terminal,  To  Strip  a  Magneto — 
Care  and  Maintenance  of  Aero  Engines:  Causes  of  De- 
fects of  Engines,  Backfiring,  Failure  to  Start,  Pre-ignition, 
Continuation  of  Firing  when  Switch  Is  "Off,"  Misfiring, 
Causes  of  Loss  of  Power — Lubricants:  System  of  Oiling  on 
Rotary  Engines — Carburetors. 

Chapter  X.    Aeroplane  and  Airship  Instruments   .    .    .    127 
Importance — ^Altimeter — Anemometer — ^Aneroid  Barometer 
— Inclinimeter — Laterometer — Pressure   Gauge — Manom- 
eter— Revolution-counter — Speed-indicator — Statoscope. 

Chapter  XL  Wireless  Telegraphy  and  Semaphore  .  .  133 
Symbols  Used  in  Diagrams  of  Wireless- telegraphy  Circuits : 
Importance,  Elementary  Principles  of  Wireless  Telegraphy, 
The  Morse  Code,  Units  of  Electricity,  The  Coulomb,  The 
Ampere,  The  Watt,  The  Joule,  The  Farad,  The  Henry,  The 
Ohm,  The  Volt,  Magnetism,  Electromagnetism,  Mutual 
Inductance,  The  Condenser,  The  Circuit,  Accumulators, 
Electric  Waves,  The  Aerial — Alphabet  and  Numeral  Signs 
— Points  to  be  Observed. 

Chapter  XII.    Aerial  Photography 152 

Importance — Camera — Focus  Lens — Ultra-violet  Rays — 
Wratten  Screen — Body  of  Camera — The  Shutter — The 
View-finder  —  Exposures  —  Plate  Slides  —  Actinometer — 
Plate  Recommended — Printing-papers  Recommended — 
Developing — Printing. 


CONTENTS 

,  PAGB 

Chapter  XIII.    Bombs   and   Bomb-dropping 162 

Types  of  Bombs — Method  of  Arming  Bombs — Method  of 
Carrying  and  Releasing  Bombs — How  to  Ascertain  Direc- 
tion of  Wind — Theory  of  Bomb-dropping — Square  Root. 

Chapter  XIV.    Night  Flying 172 

Importance — Landing  at  Night — Methods  of  Placing 
Landing-flares. 

Chapter  XV.    Artillery  Observations  from  Aircraft     .     175 
Shells  Used  by  the  Artillery — Signaling  from  an  Aeroplane 
— Location  of  Targets  and  Ranging — Ranging — Hints  for 
Artillery  Observers. 

Chapter  XVI.    Aerial  Fighting 181 

Formation  Flying — The  Flight  Leader — ^The  Flying  Officer 
— Crossing  Enemy  Lines — Signals  Between  Machines — 
Attacking  Hostile  Aircraft — Delivering  an  Attack — On 
Being  Attacked — Taking  Aim  in  the  Air. 

Chapter  XVII.    Lighter  than  Air 197 

Different  Types — Hydrogen  and  Coal-gas — Balloons — The 
Equipment  of  a  Balloon — Doping  and  Varnishing  En- 
velopes— Handling  Envelopes — Storage  of  Envelopes — 
Airship  Planes  and  Rudders — Ballonets — Size  of  Bal- 
lonets — Rigging — The  Mooring  of  an  Airship — Landing 
Skids  and  Wheels — The  Training  of  an  Airship  Pilot — 
Piloting  an  Airship — The  Maintenance  of  Gas  Pressure — 
Leaving  the  Ground — In  the  Air — Descending — Landing 
— Loss  and  Gain  of  Buoyancy. 

Chapter  XVIII.    Medical  Supervision  of  Aviators  .    .    .    213 

Appendix 219 

Definitions  and  Metric  System. 


ILLUSTRATIONS 

Bristol  Scout  (Bullet)  Frontispiece 

An  English  machine  equipped  with  8o-h.p.  Gnome  engine 
used  against  Zeppelins. 

"Baby"  Nieuport  (French),  Equipped  with  130-H.P. 

Clergett  Rotary  Engine Facing  p.    20 

German  Aeroplane  Equipped  with  Pontoons     .    .       "         58 

The  biplane  shown  is  a  German  machine  convertible  for  either 
land  or  sea  work  that  has  been  developed  since  the  beginning 
of  the  war.     It  is  being  brought  to  the  water's  edge  by  a  crane. 

Giant  Italian  Triplane "       176 

This  Caproni  triplane  can  carry  three  tons  in  addition  to  its 
own  weight  and  can  easily  accommodate  twenty-five  persons. 
It  has  a  700-h.p.  engine  and  travels  ninety  miles  an  hour.  Nine 
gims  can  be  mounted  on  the  plane,  and  in  addition  a  multitude 
of  bomb-throwing,  position-finding  and  other  devices  of  great 
utility  in  battle  and  bombarding  have  been  perfected. 


FOREWORD 

I  HAVE  read  and  studied  most  of  the  many  hand- 
books on  aeronautical  subjects  published  since  the 
outbreak  of  the  Great  War,  but,  although  I  have 
burned  much  midnight  oil,  the  book  dealing  with 
those  points  and  principles  of  aviation  which  many  of 
my  colleagues  especially  wished  to  have  was  not  to 
be  obtained.  The  majority  of  the  text-books  delved 
into  unnecessary  technicalities  and  formulae,  which 
many  of  my  aeronautical  friends  could  not  fathom 
without  much  study. 

It  was  after  spending  considerable  time  in  con- 
struction-sheds, aero-engine  shops,  and  repair  plants, 
after  graduating  as  an  aeroplane  pilot  in  the  Royal 
Naval  Air  Service,  and  after  many  months  on  the 
French,  Belgian,  and  British  battle-fronts,  with  a 
mobile  fighting  squadron,  that  I  was  requested  by 
pilot  friends  to  compile  a  handbook  that  would  meet 
the  requirements  of  the  layman  with  a  moderate 
education  who  wished  to  obtain  a  practical  knowledge 
of  flying  and  the  fundamental  principles  of  construe- 


FOREWORD 

tion,    aero-engines,    and   various   other   aeronautical 
subjects. 

For  the  most  valuable  assistance  and  corroboration 
I  wish  to  thank  the  many  contractors,  flight  lieuten- 
ants, naval,  army,  and  flight  instructors,  flight  com- 
manders, and  others  of  the  Royal  Flying  Corps  and 
the  Royal  Naval  Air  Service.  In  this  connection,  I 
shall  always  remember  with  deep  gratitude  Lieut.  J. 
W.  Langmuir  of  the  Royal  Flying  Corps  for  his  timely 
and  pointed  suggestions. 

To  those  who  wish  to  become  efficient  in  only  one 
or  two  departments  of  aerial  practice  I  would  refer 
them  to  books  dealing  with  special  subjects,  but  to 
those  who  wish  a  general  knowledge  of  aeronautical 
matters  I  submit  this  handbook  with  the  hope  that  it 
will  be  not  only  beneficial  while  training,  but  also  a 
help  and  reference  in  the  days  following  graduation. 

A.  H.  M. 

"In  the  Field,"  1917. 


THE    EYES    OF 
THE    ARMY    AND    NAVY 


THE  EYES  OF 
THE  ARMY  AND    NAVY 


AERIAL     NAVIGATION 

THE  mastery  of  aerial  navigation  is,  of  course,  the 
objective  of  every  student-pilot.  War  condi- 
tions have  emphasized  the  vital  importance  to  an 
aviator  of  a  thorough  and  intimate  knowledge  of 
flying,  combined  with  practical  experience  in  the 
use  of  map,  compass,  and  other  instruments  used  in 
aerial  navigation.  Many  tragic  occurrences  in  oversea 
flights  have  illustrated  how  priceless  an  aid  to  the 
airman  is  an  efficient  compass  and  a  knowledge  of  its 
practical  use. 

The  Compass 

It  will  be  well  to  bear  in  mind  that  the  compass 
can  give  a  pilot  only  his  direction  through  the  air;  it 


THE  EYES  OF  THE  ARMY  AND  NAVY 

is  very  inaccurate  in  regard  to  the  actual  course  that 
he  is  making  over  the  ground.  This  inaccuracy  is  due 
to  side  drift. 

In  learning  to  use  the  aeroplane  compass  the 
practical  meaning  of  the  terms  "variation," 
"deviation,"  and  "drift"  must  be  understood  by  the 
student. 

Variation 

The  working  part  of  a  compass,  which  comprises 
the  system  of  magnets,  and  card,  will,  if  undisturbed, 
take  up  a  position  with  the  north-seeking  ends  of  its 
magnets  pointing  to  the  north  magnetic  pole.  This  is 
shown  to  the  pilot  by  the  card-reading,  and  any  di- 
rection with  reference  to  this  magnetic  meridian  can 
be  ascertained  by  the  angular  markings  around  the 
card,  measured  to  the  right  from  north,  through  east, 
south,  and  west.  This  card  is  graduated  to  360°  and 
in  the  aeroplane  compass  the  last  cipher  is  generally 
omitted  to  avoid  crowding. 

The  angle  between  the  true  and  magnetic  meridians 
is  the  variation,  and  is  termed  east  or  west  variation, 
according  as  the  magnetic  meridian  is  to  the  right  or 
left  of  the  true  north.  No  satisfactory  method  of 
giving  a  "true"  reading  of  a  compass  is  possible; 
and  as  all  maps  used  for  land  work  are  based  on  the 


AERIAL    NAVIGATION  . 

true  meridian  (or  circle  joining  the  geographical  poles 
of  the  earth),  the  correction  known  as  variation  must 
always  be  determined. 

It  is  clear  that  the  appHcation  of  any  correction  is  a 


Fig.  1 


troublesome  matter  under  flying  conditions,  and  the 
omission  or  wrong  application  of  the  variation  is 
probably  the  cause  of  many  bad  "landfalls." 

3 


THE    EYES   OF    THE   ARMY   AND    NAVY 

Deviation 

Deviation  is  the  error  caused  in  a  compass  by 
the  effect  of  local  magnetic  material  used  in  the  con- 
struction of  an  aeroplane.  This  may  be  to  the  right 
or  left  of  the  magnetic  meridian,  according  to  the 


345° 


15"  West 


15°  East 


amount  of  disturbing  influences.  This  error  is  fre- 
quently very  large,  and  as  it  varies  with  the  direction 
in  which  the  machine  is  headed,  the  importance  of 
eliminating  it  altogether,  or  at  least  reducing  it  to 
moderate  proportions,  is  obvious.  This  may  be  done 
by  properly  placing  and  adjusting  the  compass. 
Nevertheless,  even  after  the  best  correction  results 
are  obtained  a  deviation  card  is  generally  made  out 
and  placed  near  the  instrument : 

4 


AERIAL    NAVIGATION 

Example:  For  Magnetic  Course 

North 4" 

Northeast 49** 

East 92* 

Southeast 137* 

South 182°  , 

Southwest 223" 

West 268** 

Northwest 312" 

North   4" 

For  example,  a  pilot  wishes  to  steer  to  a  point  in  a 
northeasterly  direction;  instead  of  steering  45°, 
he  must  steer  49°.  In  this  case  the  deviation  is  west- 
erly and  would  be  termed  4°  westerly  deviation.  It 
will  be  noticed  in  the  above  table  that  on  the  north- 
east, east,  southeast,  and  south,  westerly  deviation  is 
noticed.  A  very  good  method  of  ascertaining  whether 
the  error  is  east  or  west  is  to  memorize  the  following 
Hnes: 

Compass  best  deviation  west, 
Compass  least  deviation  east. 

For  instance,  if  the  compass  was  49**  instead  of 
45°,  the  reading  would  be  termed  best  or  greater  and 
the  deviation  would  be  west;  but  in  the  case  of  the 
reading  being  least,  the  deviation  would  be  east. 

The  first  rule  for  an  air  pilot  should  be  to  familiarize 
himself  with  the  use  of  the  compass  by  employing 

2  5 


THE  EYES  OF  THE  ARMY  AND  NAVY 

it  constantly  to  keep  his  direction.  The  majority  of 
aviators  are  without  experience  in  the  use  of  the 
rudder  for  keeping  a  steady  course  or  direction,  and 
often  the  compass  is  blamed  quite  unjustly  for  un- 
steadiness which  is  simply  due  to  bad  steering. 
However,  if  long  flights  by  compass  are  to  be  made 
with  any  certainty  the  pilot  must  be  capable  of 
steering  a  steady  course  by  the  instrument,  and 
considerable  experimenting  is  necessary  imder  all 
conditions. 


To  Lay  Off  a  Course  by  Compass 

The  courses  and  bearings  may  be  placed  in  three 
distinct  classes:  the  true  course  and  the  true  bear- 
ing, the  magnetic  course  and  the  magnetic  bearing, 
and  the  compass  course  and  the  compass  bearing. 
If  the  student-pilot  masters  the  principles  of  mapping 
out  a  true  course  and  thoroughly  understands  the 
meanings  of  the  associate  terms,  he  will  experience 
few  difficulties. 

A.  The  true  course  is  the  angle  between  the  true 
meridian  and  the  meridian  on  which  a  point  lies. 

B.  The  magnetic  course  is  the  angle  between  the 
magnetic  meridian  and  the  meridian  on  which  a  point 
lies. 

C.  The  compass  course  is  the  angle  between  the 

6 


AERIAL    NAVIGATION 


direction  in  which  the  compass  points  approximately 
north,  or  the  compass  north,  and  the  meridian  on 
which  a  point  Hes. 


MN  C  w"""** 


Consider  the  aeroplane  heading 
in  direction  D,  then: 
A  =  Magnetic  course. 
B  =  Compass  course. 
C  =  True  course. 


fig.  3 


Suppose  it  is  desired  to  steer  a  course  from  a  place 
A  to  a  place  B,  on  a  map  of  sufficiently  small 
scale  to  contain  both  places.  Join  A  and  B  with 
a  light  pencil  line  and  make  a  note  of  all  prom- 
inent places  or  objects  that  the  line  passes  over. 
Lakes,  railways,  villages,  and  large  forests  are  ex- 
cellent landmarks.  Lay  a  pair  of  parallel  rulers  along 
the  line  and  then  transfer  the  line  to  one  of  the  up- 
rights of  the  edge  of  the  map,  which  are  drawn  true 
north  and  south,  and  read  off  the  angle  the  rulers 
make  with  the  perpendicular.  This  angle  will  give  the 
true  course.  To  obtain  the  magnetic  course,  the 
mean  of  the  variations  between  the  two  points  must 

7 


THE  EYES  OF  THE  ARMY  AND  NAVY 

be  applied  and  added  or  subtracted  accordingly, 
whichever  side  of  true  north  the  variation  may  be. 
Should  there  be  any  deviation,  it  should  be  applied 
also. 

The  drawing  of  a  rough  figure  will  always  be  found 
helpful,  as  the  pilot  can  tell  at  a  glance  in  which 
direction  the  error  should  be  applied.  In  laying 
off  bearings  on  the  map  they  should  be  corrected  for 
variation  and  brought  up  to  the  true  in  the  reverse 
way. 

Thus,  if  your  compass  has  a  variation  of  15°  and 
the  magnetic  bearing  is  65°,  then  obviously  the  true 
bearing  of  the  place  must  be  65°  — 15°  =  50°. 

To  Lay  Off  a  Course,  Allowing  for  Drift 

Suppose  a  pilot  wishes  to  travel  from  A  to  B 
and  the  magnetic  course  is  65°,  the  speed  of  the  ma- 
chine is  60  knots  an  hour  and  the  wind  direction  is 
southeast  (which  is  135°  true). 

Lay  off  a  line  A-B  in  the  direction  required  (65° 
magnetic  bearing).  From  A  set  off  a  line  in  the 
direction  of  the  wind  (135°  true),  and  mark  off  on  the 
Hne  a  point  equal  to  an  hour's  wind  speed  upon  the 
line  A-C.  This  should  be  applied  from  a  scale 
already  decided  upon. 

Set  the  dividers  at  an  hour's  speed  of  the  aircraft, 

8 


AERIAL    NAVIGATION 


applying  the  same  scale,  and  from  the  point  C  cut 

the  line  A-B  with  an  arc  and  mark  this  point  D. 

Join  the  two  points  C-D.     Next  draw  the  true  north- 

and- south  line  through  the 

point   C,   and   by   placing   a 

protractor  on  the  north-and- 

south    line,    centrical,  at    the 

point  C,  the  angle  the 

line  C-D  makes  is  the 

true  course. 


applying  variation  and 
deviation  (if  any)  the 
magnetic  course  or 
compass  course  can  be 
obtained. 

In  the  example  the 
variation  is  15°  west, 
and,  being  west,  it  is 
added  to  the  true 
reading. 

It  should  be  remem- 
bered that  in  the  first 
course  the  wind  was  not  considered,  and  to  get  from  A 
to  B  it  was  necessary  to  steer  65°  magnetic  or  50° 
true.    But  when  the  wind  is  to  be  taken  into  account 

9 


THE  EYES  OF  THE  ARMY  AND  NAVY 

it  will  be  readily  observed  that  it  is  necessary  to  steer 
79°  magnetic  or  64°  true  if  the  pilot  wishes  to  fly 
straight  on  the  course  A-B.  The  horizontal  and 
vertical  lines  through  the  point  A  are  only  guide- 
lines to  insure  the  correct  placing  of  the  protractor 
when  mapping  out  the  direction  of  the  wind.  The 
line  A-D  is  the  ground  speed  for  one  hour  of 
flight.  By  ascertaining  the  length  of  the  line  D-B 
and  applying  it  to  the  ground  speed,  the  time  it 
would  require  to  cover  the  distance  A-B  is  obtained. 
Assuming  that  the  correct  calculation  regarding 
the  velocity  of  the  wind  and  the  velocity  of  the  ma- 
chine has  been  obtained,  if  the  pilot  steers  the  cor- 
rect course,  the  machine  should  pass  over  the  land- 
marks already  selected.  A  very  good  rule  to  follow 
is  to  take  bearings  of  certain  objects  in  the  range  of 
vision  from  the  map  before  a  pilot  starts  out,  and 
as  the  journey  is  undertaken  the  course  may  be 
checked  from  time  to  time. 

To  Ascertain  Position 

A  position  of  an  aircraft  can  be  obtained  by  taking 
bearings  of  an  object  ahead  and  slightly  to  one  side 
of  another  object  abeam  or  a  little  abaft  the  beam, 
and  where  these  two  lines  cross  is  the  position  of  the 
aeroplane. 

10 


AERIAL    NAVIGATION 

The  bearing  of  point  X  is  70°  true  and  the 
bearing  of  point  Z  is  150°  true.  Place  the  protract- 
or, centrical,  at  the  point  X  and  mark  off  the 
true  bearing.  Produce  the  line  through  the  point. 
Carry  out  this  same  procedure  on  the  point  Z 
and  by  ascertaining  the  latitude  and  longitude  of 
the  point  where  the  lines  cross,  the  exact  position  is 
obtained. 

Parallels  of  latitude  are  obtained  from  the  north 
and  south  edges  of  the  chart  or  map,  and  longitude 
from  the  meridians  given  at  the  top  and  bottom  of  the 
chart  or  map. 

Consideration  of  Wind 

In  calculating  courses  where  wind  is  to  be  con- 
sidered it  is  absolutely  necessary  to  have  a  knowledge 
of  the  increase  in  velocity  of  the  wind  and  the  veer- 
ing and  backing  as  height  is  attained. 

Veering  of  the  Wind 

When  a  wind  is  said  to  "veer,"  one  means  that  it  is 
moving  around  in  a  clockwise  direction,  and  to  "back" 
indicates  that  the  motion  is  in  an  anti-clockwise  di- 
rection; however,  in  the  northern  hemisphere  the 
wind  seldom  "backs,"  and  in  all  calculations  it  is 

n 


THE  EYES  OF  THE  ARMY  AND  NAVY 

advisable  to  allow  for  veering  at  the  following  aver- 
age: 

At  i,ooo  feet  the  wind  veers  io° 

At  2,000  feet  the  wind  veers  15° 

At  3,000  feet  the  wind  veers  20° 
Above  this  height  the  wind  remains  practically  con- 
stant. 

At  1,000  feet  the  velocity  of  the  wind  increases  to 
one  and  a  half  times  its  own  velocity. 

At  2,000  feet  the  velocity  of  the  wind  increases  to 
twice  its  own  velocity. 

Above  2,000  feet  there  is  practically  no  increase. 
In  the  aeronautical  school  the  speed  of  the  wind  is 
always  given  in  force  numbers  as  indicated  by  the 
Beaufort  Scale. 

BEAUFORT  WIND  SCALE 

Faru  Velocity  in  Nautical  Miles  per  Hour 

1 1-3 

2 4-6 

3 7-10 

4 11-16 

5 17-21 

6 22-27 

7 28-33 

8 34-40 

9 41-47 

lo 48-55 

12 


AERIAL    NAVIGATION 
How  to  Ascertain  the  Radius  of  Action  of  an  Aeroplane 

If  a  pilot  is  ordered  to  scout  in  a  certain  direction 
and  the  machine  has  petrol-supply  for  a  given  time, 
with  a  little  calculation  a  pilot  can  ascertain  the 
correct  time  to  commence  the  return  journey  and 
the  position  reached.  If  the  expedition  is  under- 
taken on  a  comparatively  calm  day,  the  pilot  can 
ordinarily  fly  in  the  direction  ordered  for  half  the 
time  of  petrol-supply  and  then  return ;  but  when  the 
wind  is  to  be  taken  into  account  a  calculation  is 
necessary. 

Example. — A  pilot  is  ordered  to  scout  in  a  north- 
easterly direction,  the  machine  has  petrol-supply  for 
five  hours,  and  the  wind  is  south.  The  order  is  given 
to  a  pilot  and  it  is  for  him  to  work  out  the  problem. 
First  it  is  necessary  for  him  to  ascertain  the  speed 
of  the  wind  and  decide  the  height  at  which  he  will 
carry  out  the  scouting  patrol.  Suppose  the  wind  is 
9  knots  an  hour  and  the  pilot  decides  to  fly  at  3,000 
feet.  The  upper  wind,  or  the  wind  at  the  height  men- 
tioned, will  be  twice  the  velocity,  which  will  be  18 
knots  and  will  veer  20°.  Therefore,  instead  of  the 
wind  being  in  a  direction  southeast  (135°  true)  it  will 
be  155°  true. 

Now  that  the  direction  and  speed  of  the  upper 
wind   has   been   obtained  and   the  pilot  knows   the 

13 


THE  EYES  OF  THE  ARMY  AND  NAVY 


speed  of  his  machine  (say  60  knots  an  hour),  he  can 
work  out  the  problem. 

Draw  a  Hne  A-B  in  a  northeasterly  direction; 
select  a  point  E,  approximately  half-way  along  the 
line.  From  this  point  E  draw  the 
wind  line  E-C  to  a  scale  decided 
upon.  The  E-C  line  should  indicate 
an  hour's  speed  of  the  wind — 18  knots. 
Set  the  dividers  at  60  knots, 
the  speed  of 
the  machine 
for  one  hour, 
according  to 
scale,  and  set 

4 


c° 


^f^ 


00; 


V 


Fig.  5 


one  point  of  the  dividers  at  the  point  C  and  cut  the  line 
E-B.  Mark  the  point  obtained  D.  From  the  point  C, 
mark  off  a  similar  distance  to  cut  the  line  E-A,  and  mark 
the  point  where  the  E-A  line  is  cut  F.     Connect  the 

14 


AERIAL    NAVIGATION 

points  C-D  and  C-F.  Draw  the  north  line  through 
C,  and  the  angle  the  line  C-D  makes  is  the  course 
out,  and  the  angle  the  line  C-F  makes  is  the  course 
returning.  E-D  is  the  ground  speed  out,  and  E-F  the 
ground  speed  on  the  return  journey.  These  two 
speeds  should  be  termed  G.i  and  G.2,  respectively, 
and  by  applying  the  following  formula  the  radius  of 
action  is  obtained: 

Radius  of  action  =  Time  X  G.i  X  G.2 
Time  to  turn         =   Radius 

In  the  example  the  time  is  five  hours,  G.i  is  62 
miles  and  G.2  is  52  miles,  therefore: 


R  = 


5  X  62  X  52 

62-1-52       =   141.4 

_.  141  =  2  hours  17  minutes 

Tmie  to  turn  =    — -  ,  .      ,  ,  x 

02  (approxmiately) 

If  a  pilot  desires  to  ascertain  the  position  reached, 
all  that  is  necessary  is  to  apply  the  time  out  and 
locate  the  position.  For  instance,  if  the  time  to 
turn  is  two  hours,  measure  twice  the  ground  speed 
out  on  the  E-B  line  produced,  and  the  point  reached 
is  the  point  of  turning  or  should  be  if  the  pilot  has 
calculated  correctly. 

15 


THE    EYES    OF    THE    ARMY   AND    NAVY 
Radius  of  Action  and  Returning  to  a  Different  Position 

To  scout  in  a  given  direction  and  return  to  another 
point,  or  to  a  seaplane  carrier  steaming  in  a  given 
direction,  is  an  order  that  often  appears  when  on 
seaplane  duty,  and  quite  occasionally  land-machine 
pilots  are  ordered  to  patrol  an  area  in  a  certain  di- 
rection and  return  to  an  aerodrome  many  miles  from 
the  home  station. 

Example. — Scout  in  a  direction  northeast  and  re- 
turn to  a  point  eighty  miles  north. 

The  pilot  ascertains  the  direction  of  the  wind  and 
the  force.  He  decides  to  fly  at  4,000  feet.  Suppose 
the  surface  wind  is  Force  3,  at  the  height  mentioned 
it  would  be  approximately  18  knots  and  would  veer 
20°.  Suppose  the  wind  is  from  the  south  and  it 
veers  the  20°,  it  would  be  20  west  of  south.  The 
speed  of  the  machine  is  60  knots  an  hour  and  has 
petrol-supply  for  four  hours. 

Draw  a  line  A-B  in  the  direction  named  and  then 
the  wind  line  A-C.  From  C  set  off  an  hour's 
speed  of  the  machine  and  mark  the  point  where  the 
A-B  is  cut  D. 

From  A  draw  a  line  north  (true)  and  measure  off 
(to  scale)  80  miles.  Mark  the  point  F.  The  machine 
has  petrol-supply  for  four  hours,  therefore,  as  one  hour 
is  being  considered  in  the  problem,  mark  off  a  point 

16 


AERIAL    NAVIGATION 


equal  to  one-fourth  cf  the  60  miles  from  A  along 
the  line  A-F.  Mark  the  point  obtained  G.  From 
D  produce  a  line  through  G  and  a  distance"^  be- 
yond. Set  the  dividers  at  60  knots,  the  speed  of 
the  machine  for  one 
hour,  and]  from  the 
point  C  cut  the  pro- 
duced line  from  G  and 
mark  the  point  H- 
From  this  point  draw 
a  line  to  the  point  C. 
Set  the  parallel  rulers 
along  the  line  H-A  and 


transfer  the  line  to  cut  the  point  F.  Where  the  line 
cuts  the  A-B  line  is  the  actual  point  of  turning. 
Mark  this  point  J.  By  drawing  a  true  north  line 
through  the  point  C  and  applying  variation  or  de- 

17 


THE  EYES  OF  THE  ARMY  AND  NAVY 

viation  (if  any)  the  magnetic,  or  compass,  course 
can  be  obtained. 

The  line  A-D  is  the  ground  speed  out  for  one 
hour. 

The  line  C-D  is  the  magnetic  course,  assuming 
that  the  magnetic  course  is  desired  and  the  correct 
applications  have  been  made. 

The  line  C-H  is,  likewise,  the  course  to  steer  for  the 
return  journey. 

The  hne  H-A  is  the  ground  speed  for  one  hour  on 
the  return  trip.  The  transferred  line  F-J  is  the  actual 
track  returning. 

This  problem,  as  also  the  proceeding  radius  of 
action  problem,  can  be  proved  by  applying  the 
ground  speed  along  the  track  line.  If  the  figure  has 
been  worked  out  correctly,  the  ground  speed  should 
correspond  with  the  number  of  hours  of  petrol- 
supply;  but  care  should  be  taken,  when  proving 
figures,  that  the  correct  lines  are  applied.  In  the  last 
example  the  line  A-D  should  only  be  applied  along 
the  line  A- J,  and  then  the  line  A-H  should  be  applied 
along  the  line  J-F. 

Thirty  minutes  instead  of  an  hour  may  be  taken 
in  all  the  above  problems,  as  long  as  the  pilot  bears 
in  mind  that  only  thirty  minutes  is  being  considered 
throughout  and  applies  the  scale  accordingly.  In 
my  experience  of  mapping  out  courses  I  have  found 

i8 


AERIAL    NAVIGATION 

that  one  hour  is  the  most  advisable  to  use,  as  much 
calculation  is  thereby  eliminated. 


Radius  of  Action  Returning  to  a  Seaplane  Carrier 
Steaming  in  a  Given  Direction 

A  pilot  is  ordered  to  scout  in  a  northeasterly  di- 
rection and  to  return  to  a  carrier  which  is  steaming 
south  at  15  knots  an  hour.  Wind  is  from  the  north- 
west and  the  machine  has  petrol-supply  for  four 
hours.  Suppose  the  expedition  is  carried  out  at 
4,000  feet  and  the  surface  wind  is  10  miles  an  hour. 
At  the  height  mentioned  it  would  veer  over  20°  and 
be  twice  its  surface  velocity;  therefore  it  would  be 
from  a  direction  335°  and  the  strength  would  be  20 
miles  an  hour. 

Draw  a  line  A-B  in  the  direction  named  and  from 
A  draw  a  line  south,  and  produce  this  line  a  short 
distance  north  of  A.  On  this  line  produced  mark  off 
a  distance  equal  to  an  hour's  speed  of  the  carrier; 
mark  this  point  C.  From  C  mark  off  the  wind 
C-D.  From  D  set  the  dividers  at  the  speed  of  the 
aircraft  for  one  hour,  take  60  knots,  and  cut  the 
line  A-B.  Mark  the  point  obtained  F.  Join  C  and  F, 
and  D-F.  From  A  measure  the  distance  that  the 
carrier  would  cover  in  four  hours  and  mark  off  this 
distance  on  the  south  line  from  A.    Indicate  the  po- 

»9 


THE  EYES  OF  THE  ARMY  AND  NAVY 

sition  obtained  H.  Set  the  parallel  rulers  on  the 
C-F  line  and  transfer  the  line  to  cut  the  point  H,  and 
where  this  line  cuts  the  A-B  line  indicates  the  time 
of  turning.  Draw  a  true  north  line  through  the  point 
D,  and  apply  variation  and  deviation  if  magnetic  or 
compass  course  is  desired.  D-F  is  the  course  line; 
C-F  the  ground  speed  out  for  one  hour.    Produce  the 


ots® 


©a' 


cK 


Fig.  7 


.H 


■».'.  .-,.   .'I; 


AERIAL    NAVIGATION 

line  F-C  and  from  the  point  D  cut  this  line  with 
an  hour's  speed  of  the  aircraft.  Mark  this  point  P. 
Join  the  points  D-P  and  A-P.  The  line  D-P  is  the 
return  coiirse  line,  and  the  Hne  A-P  the  ground  speed 
for  one  hour  on  the  return  journey.  In  all  problems 
where  a  ship  steaming  in  a  given  direction  has  to  be 
considered,  it  is  necessary  to  reverse  the  ship's  speed 
(the  Hne  A-C  in  the  example)  in  order  to  bring  the 
ship  at  rest  to  allow  for  calculation  of  wind.     (Fig.  7.) 

To  Intercept  an  Enemy  Machine 

This  order  is  a  very  common  one  on  active  service 
and  when  on  coastal  patrol.  An  enemy  machine  is 
reported  to  be  flying  over  a  position  100  miles  south- 
east of  your  location  and  steering  in  a  northeasterly 
direction.  You  are  ordered  to  intercept  the  machine. 
(Fig.  8.) 

Mark  your  location  A  and  draw  a  line  southeast 
(true,  unless  otherwise  stated).  To  a  scale  mark 
the  position  100  miles  southeast  B.  Draw  a  line  of 
indefinite  length  in  a  northeasterly  direction  and 
mark  the  farthest  point  C.  From  B  set  the  distance 
equal  to  an  hour's  speed  of  the  enemy  aircraft.  In 
this  case  we  will  take  60  knots.  Mark  the  point  ob- 
tained D.  Set  the  dividers  at  one  hoiu-'s  speed  of 
your  own  machine,  take  75  knots,  and  set  one  point 

3  21 


THE  EYES  OF  THE  ARMY  AND  NAVY 

of  the  dividers  at  the  point  D  and  cut  the  line  A-B. 
Mark  the  position  obtained  H.  Join  D  to  H.  From 
the  point  A  draw  a  line  parallel  to  the  line  H-D,  and 
where  this  line  cuts  the  B-C  line  is  the  point  of  inter- 


rig.8 


ceptance.  Mark  the  point  Q.  A-Q  is  the  course,  and 
as  the  wind  is  not  taken  into  account  it  is  also  the 
track.  H-D  is  the  ground  speed  for  one  hour;  there- 
fore H-D  into  A-Q  will  give  the  time  to  intercept. 
In  problems  of  this  natiire  the  wind  is  seldom  taken 
into  account,  as  the  enemy  machine  is  also  affected. 


II 

THEORY   OF   FLIGHT 

IN  the  study  of  theory  of  flight  many  formulae 
are  necessary  to  gain  a  comprehensive  knowledge 
of  the  various  lift  and  drift  coefficients  and  to  learn 
how  to  apply  the  coefficient  curves.  This  chapter 
deals  only  with  a  brief  description  of  the  action  of  a 
stream  of  air  on  different-sized  planes  and  gives  only 
a  general  outline  of  the  dynamics  of  an  aeroplane. 

Pressure 

The  pressure  of  the  atmosphere  is  due  to  the  weight 
of  the  atmosphere;  it  is  usually  measured  by  the 
height  of  a  column  of  mercury.  At  mean  sea-level,  at 
a  temperature  of  32°  Fahrenheit,  the  normal  pressure 
is  29,9  inches  of  mercury;  under  the  same  circum- 
stances, at  sea-level,  the  weight  of  a  cubic  foot  of  air 
is  .08  pound.  The  pressure  of  the  atmosphere  is 
affected,  to  a  moderate  extent,  by  both  temperature 
and  humidity.  When  the  atmosphere  is  in  motion 
there  is  a  large  mass  of  air  under  weight,  and  in  this 

23 


THE  EYES  OF  THE  ARMY  AND  NAVY 

condition  it  possesses  considerable  energy  and  is  capa- 
ble of  exerting  force.  By  the  use  of  aero-engines  the 
air  is  put  into  motion  and  similar  energy  is  obtained. 


The  Action  of  Pressure  on  a  Flat  Plate 

If  a  flat  plate  is  towed  at  right  angles  to  a  stream 
of  air  the  stream  will  be  deflected  and  will  flow  over 
the  edges  of  the  plate  and  will  unite  again  a  consid- 
erable distance  to  the  rear.  To  the  immediate  rear  of 
the  plate,  eddies  will  be  formed,  and  on  the  front  part 
of  the  plate  a  pressure  will  be  exerted.  This  pressure 
and  the  eddies  formed  will  cause  a  drop  in  the  general 
pressure;  therefore  the  force  necessary  to  keep  up  a 
steady  forward  motion  of  the  plate  will  depend  on 


Fig.  9 

the  difference  of  the  absolute  pressure  between  the 
two  sides  of  the  plate.  The  total  pressure  will  also 
be  influenced  by  the  length  of  the  edge  of  the  plate, 
the  point  of  greatest  pressure  being  near  the  center 
of  the  plate.     (Fig.  9.) 

The  resistance  to  forward  motion  varies  as  the  ve- 

24 


THEORY   OF    FLIGHT 

locity  squared;  generally  written  V^.  If  a  plate  of 
one  square  metre  is  towed  at  the  rate  of  one  metre  a 
second  a  resistance  of  .08  kilo  will  be  set  up;  there- 
fore for  calculation  of  the  power  wasted  by  the  detri- 
mental surface  of  an  aeroplane  the  following  formula 
is  used : 

R  =  .08  X  A  X  V^  and 

R    =  Resistance. 
.08  =  Unit  of  resistance. 
A    =  Area  of  supporting  or  lifting  surface. 
V^  =  Velocity  squared. 

The  term  "detrimental  surface"  includes  the  fuse- 
lage, landing-chassis,  struts,  wires,  pilot,  and  in  fact 
all  those  parts  which  do  not  help  in  the  Hft,  but  on 
the  contrary  retard  the  progress  of  the  machine. 

Lift  Over  Drift  Ratio 

On  a  flat  plate  the  "lift  over  drift"  ratio  may  reach 
a  fairly  high  value,  but  its  value  is  small,  while  the 
lift  coefficient  is  sufficiently  large  for  ordinary  pur- 
poses. The  negative  pressure,  or  suction,  upon  the 
upper  surface  of  a  wing  section  provides  not  less  than 
75  per  cent,  of  the  total  lift.  There  is  a  critical  angle 
above  which  the  negative  pressure  on  the  upper 
surface  becomes  uniform,  while  the  pressure  on  the 
lower  surface  falls  off.    The  effect  is  to  cause  a  sudden 

2$ 


THE  EYES  OF  THE  ARMY  AND  NAVY 

decrease  in  the  total  lift,  coupled  with  a  sudden  increase 
in  the  drift.  At  an  angle  of  incidence  less  than  2° 
the  pressure  upon  the  lower  surface  vanishes  and  be- 
comes negative. 

Aspect  Ratio 

Aspect  ratio  is  the  porportion  that  the  length  of 
the  plate  or  plane  bears  to  the  width.  A  stream  of 
air  naturally  follows  the  path  of  least  resistance; 


Fig.10 

GOOD  ASPECT   RATIO 


therefore  it  will  not  only  attempt  to  escape  over  the 
forward  and  rear  edges  of  the  plate,  but  also  over  the 


.ri9.11 

POOR  ASPECT   RATIO 


sides.    This  leakage  means  loss  of  power.    In  the  Fig. 
10  it  will  be  readily  observed  that  the  plate  suffers  very 

26 


THEORY   OF    FLIGHT 

little  from  the  leakage  on  account  of  the  good  aspect 
ratio,  but  in  the  Fig.  ii  the  leakage  is  very  pro- 
nounced. 

In  the  above  paragraphs  a  flat  plate  towed  at  right 
angles  with  the  stream  of  air  has  been  considered 
throughout.    If  a  fiat  plate  is  inclined,  the  stream  lines 


will  follow  the  underneath  part  of  the  plate  closely, 
but  will  be  deflected  to  a  considerable  degree  at  the 
top  surface,  and  an  eddy  field  will  result.  A  suction 
or  negative  pressure  is  set  up  by  the  eddies,  which  in- 
crease the  total  resistance  to  a  large  extent.  In  order 
to  overcome  this  eddy  field,  curved  planes  are  used 
for  all  aeroplane  work.     (Figs.  12  and  13.) 

Center  of  Pressure 


It  will  be  observed  that  in  a  flat  plane  the  center  of 
pressure  is  in  the   middle  of  the  plane  at    approxi- 

27 


THE  EYES  OF  THE  ARMY  AND  NAVY 

mately  ninety  degrees,  and  moves  nearer  to  the  lead- 
ing edge  as  the  angle  of  incidence  decreases ;  however, 
in  a  curved  plane  the  center  of  pressure  follows  a  more 
complex  law.  In  a  curved  plane  the  center  of  pressure 
is  also  at  the  middle  of  the  plane  at  the  same  angle 
as  the  fiat  plane,  but  it  gradually  approaches  the  lead- 
ing edge  until  the  angle  of  thirty  degrees  is  reached; 
it  then  moves  abruptly  until  the  angle  of  incidence  is 
slightly  above  fifteen  degrees,  when  it  approaches  the 
trailing  edge  rapidly.  Therefore  it  should  be  borne 
in  mind,  in  considering  ordinary  angles  of  incidence 
used  in  aviation,  that  when  the  angle  of  incidence  de- 
creases in  a  flat  plane  the  center  of  pressure  moves 
toward  the  leading  edge,  and  in  a  curved  plane  the 
center  of  pressure  moves  toward  the  trailing  edge. 

The  Advantages  of  Curved  and  Flat  Planes 

The  Hft  or  pressure  which  the  wind  exerts  on  any 
plane  is  due  to,  and  is  a  measure  of,  the  downward 
momentum  of  the  mass  of  air  dealt  with  by  the 
•plane. 

In  the  curved  plane  the  air  is  not  only  given  a  more 
downward  trend,  but  it  is  given  this  downward  trend 
with  far  less  eddying. 

The  effect  is  that  a  bigger  vertical  momentum  is 
produced  with  actually  less  resistance;   thus  the  effi- 

28 


THEORY   OF    FLIGHT 

ciency  of  a  properly  designed  curved  plane  is 
immensely  greater  than  that  of  a  simple  fiat  plane. 

It  is  of  great  importance  to  notice  that,  whether  in 
the  fiat  plane  or  the  curved  plane,  the  lower  and  the 
upper  surfaces  each  contribute  to  drive  the  air  down- 
ward ;  when  the  plane  is  set  at  an  angle  to  the  air,  the 
under  surface  by  directly  forcing  the  air  to  take  a 
downward  path  and  the  upper  surface  by  the  force  of 
suction  or  negative  pressure,  of  the  total  lift  thus 
derived  at  ordinary  small  angles  of  incidence  about 
70  per  cent,  is  due  to  this  suction  on  the  top  siu*face. 

When  the  top  surface  is  divided  from  the  bottom 
surface,  as  is  practically  always  the  case  in  modem 
aeroplanes,  the  lifts  due  to  each  surface  are  practically 
independent  of  one  another;  that  is  to  say,  we  can 
have  a  fiat  or  convex  or  concave  under  surface  without 
altering  the  characteristics  of  the  upper  surface  ap- 
preciably ;  conversely,  we  could  alter  the  camber  of  the 
upper  surface  considerably  without  affecting  the  lift 
due  to  the  under  surface  appreciably. 

Stream  Line 

In  aeroplanes,  as  in  airships,  the  object  is  to  present 
as  Uttle  resistance  to  forward  motion  as  possible; 
therefore  all  the  materials  are  made  smooth,  projec- 
tions eliminated,  and  the  various  parts  which  go  to 

29 


THE  EYES  OF  THE  ARMY  AND  NAVY 

make  up  a  complete  aeroplane  stream-lined.  By 
stream-lined  is  meant  that  a  body  must  be  so  shapecf 
that  when  it  strikes  or  is  struck  by  a  current  of  air 
very  few  eddies  are  caused.  It  has  been  proved  con- 
clusively that  for  low  speeds  the  shape  of  the  rear  part 
of  the  body  is  more  important  than  the  front.  The 
reason  of  this  is  that  the  air  is  easily  split  asunder  with 
little  eddjring,  but  if  it  is  to  be  united  again  evenly, 
without  eddies  in  the  rear,  the  sides  of  the  body  must 
be  carefully  shaped  to  lead  the  air  to  unite. 

If  the  trailing  edges  of  the  body  are  not  stream- 
lined, the  air  streams  do  not  unite  until  some  distance 


Fig.14 


NON-STREAM  LINE 


Fig. 15 

STREAM   LINE 


behind  the  body.  In  this  space,  namely,  between  the 
body  and  where  the  currents  unite,  eddies  are  formed ; 
to  form  these  needs  an  expenditure  of  energy.  For 
this  reason  it  will  be  seen,  on  looking  at  an  aeroplane, 
that  all  spars  and  struts  are  placed  blunt-edged  for- 
ward and  stream-lined  in  rear.     (Figs.  14  and  15.) 


The  Dynamics  of  an  Aeroplane 

If  a  wing  section  or  aerofoil  is  towed  through  air, 
disturbances  are  set  up.    These  distwbances  are  of  a 

30 


THEORY    OF    FLIGHT 

very  complex  character  and  the  nature  of  them  de- 
pends upon  the  shape  of  the  wing  section,  its  presenta- 
tion to  the  air  current,  and  a  few  minor  factors. 

The  general  trend  of  the  air  is  in  a  downward  direc- 
tion. When  matter  has  velocity  imparted  to  it,  it  is 
said  to  possess  momentum.  This  momentum  is 
measured  by  the  product  of  the  mass  of  the  matter 
and  its  velocity.  The  force  necessary  to  impart  this 
momentum  is  equal  to  the  amount  of  momentum 
imparted  to  the  matter  in  unit  time.  For  instance, 
if  a  wing  section  deals  with  a  mass  of  air  A  pounds  in 
one  second  and  gives  to  the  mass  of  air  a  vertical 
downward  velocity  of  B  feet  a  second,  then  it  is  ob- 
vious that  the  force  necessary  to  create  this  air  dis- 
turbance is  A  pounds  x  B  feet  and  it  will  be  readily 
observed  that  the  upward  reaction  on  the  wing  must 
also  be  equal  to  AB. 

In  addition  to  the  downward  velocity  imparted  to 
a  mass  of  air  by  the  moving  plane,  which  produces 
lift,  there  is  also  a  certain  amount  of  relative  forward 
motion  given  to  the  air,  due  to  the  angle  of  incidence 
and  the  sldn  friction.  This  reaction  is  called  resist- 
ance, or  the  drift  of  a  plane.  Therefore  the  most  effi- 
cient lifting  surface  is  one  in  which  the  upward  force 
per  unit  area  of  surface  is  large,  while  the  resistance 
or  drift  is  comparatively  small.  In  order  to  maintain 
flight  the  power  supplied  to  an  aeroplane  has  to  be 

31 


THE  EYES  OF  THE  ARMY  AND  NAVY 

great  enough  to  overcome  the  resistance  set  up  by  the 
wings,  and  to  provide  siifficient  extra  thrust  for  the 
body  and  all  other  non-lifting  surfaces. 


Lift  and  Drift  on  a  Wing  Section  in  Motion 

In  Fig.  i6  a  wing  section,  whose  chord  is  inclined  at 
an  angle  S  to  the  direction  of  motion,  is  represented. 
S  is  the  angle  of  incidence.  V  indicates  the  speed  of 
the  air  relative  to  the  machine  or  the  actual  speed 


of  the  aeroplane  when  flying  in  still  air.  Z-Y  repre- 
sents the  lift  on  the  plane,  while  0-Y  indicates  the  drift 
or  resistance  to  motion.  E-Y  is  the  resultant  force 
on  the  wing  section  and  is  incHned  to  the  direction 
of  the  lift  at  the  angle  E-Y-Z,  v^hich  is  equal  to  G, 
the  gliding  angle ;  for  the  particular  wing  section  and 
angle  of  incidence.  Y,  the  point  at  which  the  resultant 
force  cuts  the  chord,  is  the  point  of  the  center  of 
pressure.  This  point  varies  with  the  angle  of  inci- 
dence, and  is  described  under  "center  of  pressure." 

32 


THEORY   OF    FLIGHT 
Loading 

The  loading  of  an  aeroplane  is  the  weight  carried 
per  unit  area  of  .supporting  surface;  therefore  if  W 
equals  the  total  weight  of  a  machine  and  A  is  the 
area  of  supporting  surface, 


W 

Loading  =     . 

A. 

Example: 

Weight  of  machine  is  2,000  pounds 

Area 500  square  feet 

=  Loading  =  4  lbs.  per  sq.  foot 

The  loading  is  always  constant  for  a  given  machine. 


Weight  =  Lift 

In  horizontal  flight  the  lift  on  the  wing  of  an  aero- 
plane must  be  exactly  equal  to  the  weight  of  the 
machine;  therefore,  W=  L. 

The  Gliding  Angle 

A  machine  gliding  at  its  correct  gliding  angle  is 
under  the  same  conditions  as  when  flying  level.  In 
Fig.  17a  machine  gliding  is  represented. 

L-K  is  the  gliding  path.  J-M  represents  the  total 
weight  which  replaces  the  thrust  of  the  engine;  there- 

33 


THE  EYES  OF  THE  ARMY  AND  NAVY 

fore  it  is  equal  to  the  total  resistance  of  the  machine 
at  the  particular  angle  of  incidence  at  which  the 
machine  is  flying.    J-X  is  the  component  of  the  weight 


perpendicular  to  the  flight  path  and  practically  equal 
to  the  weight.    Therefore, 

_,. ,.            ,         Total  Resistance 
Gilding  angle  =         ^^^^^ 

The  point  of  minimum  total  resistance  gives  the 
flattest  gliding  angle. 

How  to  Ascertain  Visibility  of  Horizon 

Visibility  of  height  =  i.i5y/H 

Note:  (For  explanation  of  square  root "/  "  see  "The  Applica- 
tion of  Square  Root "  under  chapter  dealing  with  bombs  and  bomb- 
dropping.) 

34 


THEORY   OF    FLIGHT 


LIFT  AND   DRIFT   CO-EFFICIENT,  AND   AERO- 
DYNAMICAL EFFICIENCY  CURVES 


Fig.18 

"~^ 

.0? 

20 

018 

/ 

\ 

18 
16 
14 

016 

/ 

\ 

.014 

4 

V 

.012 

f- 

^J 

12 

.010 
.08 

1 

\ 

10 
'8 

1 

■  "   x 

\ 

\ 

y 

.06 
04 

/ 

/    / 

V 

< 

6 
4 

/ 

V 

/ 

\, 

.02 
0 

/ 

/ 

N 

2 

5°         10°         15°        20° 

Lift  Co-efficient. 


Drift  Co-efficient. 
••  Kx  " 


Aerodynamical  Efficiency. 
"A.E" 


Angle  of  Incidence 

The  maximum  value  of  Lift  Co-efficient  is  from  .oi8  to  .02,  and 
occurs  at  15  degrees  angle  of  incidence. 

The  maximum  Aerodynamical  Efficiency  is  just  over  14,  and  occurs 
at  4  degrees  to  6  degrees  angle  of  incidence. 


35 


THE  EYES  OF  THE  ARMY  AND  NAVY 

Example:    An  aeroplane  is  flying  at  a  height  of 
8,ioo  feet;   find  visibility  of  horizon. 

Visibility  of  horizon  =  1.15^8100 
Square  root  of  height  is  90,  therefore  visibility  of  height    = 
1. 15  X  90  =  103.5  miles 


Miscellaneous  Formulae 

To  ascertain  the  weight  of  a  machine: 
W  =  Ky    p    A    V2 


W    =  Weight. 

Ky  =  Lift  co-efficient. 

p      =  Density  of  air  (usually  .08  lbs.  per  cubic  ft.) 

A     =  Area  of  wing  surface. 

V^    =  Velocity  squared. 

W 
Area  of  wings  =  A  =^^   p   A  V^ 

„    .  drift  Kx 

Resistance  =   — r-— -  =  r^- 

weight       Ky 

Velocity       =    v/z^ight 
^  Kyp  A 
Thrust  =  (approximately)  ^  of  weight. 

Stalling  speed  =    J  i25^ 
"     Ky  p 


Ill 

MAP-READING 

IT  is  not  necessary  for  a  pilot  to  have  an  extensive 
knowledge  of  this  subject,  but  the  meanings  of 
the  various  conventional  signs  that  are  used  on  ser- 
vice maps  and  nautical  charts,  and  a  knowledge  of 
how  to  apply  a  scale  of  a  map,  are  absolutely  essen- 
tial. The  scale  of  a  map,  sketch,  or  plan  is  used  to 
denote  the  proportion  that  a  distance  between  any 
two  points  on  a  map  bears  to  the  distance  between 
the  same  two  points  on  the  ground.  For  instance, 
if  the  distance  between  two  towns  on  a  map  is  one 
inch  and  the  distance  on  the  ground  is  two  miles  the 
scale  may  be  said  to  be  one  inch  to  two  miles.  The 
scale  of  a  plan  is  dependent  upon  the  amount  of 
detail  which  has  to  be  shown.  In  the  case  of  plans 
of  houses,  fortifications,  and  earthworks  the  scale 
would  be  a  large  one,  whereas  in  sketches  of  roads, 
routes,  and  positions  the  scale  would  be  small. 

There  are  various  methods  of  showing  the  scale. 
On  a  plan  it  may  be  stated  that  the  scale  is  "so  many 
4  37 


THE  EYES  OF  THE  ARMY  AND  NAVY 

inches  to  the  mile,"  or  "so  many  miles  to  the  inch." 
What  is  known  as  a  representative  fraction  (R.  F.) 
may  be  used.  In  this  case  the  numerator  is  always 
one  unit  and  the  denominator  is  expressed  in  similar 
units.  The  latter  shows  the  length  of  a  line  on  the 
ground  which  is  represented  by  the  former  on  the 
plan.  The  unit  may  be  an  inch,  a  foot,  a  yard  or  a 
metre. 

For  instance,  if  the  R.  F.  is  -^o  it  means  that  one 
inch  on  the  map  represents  50  inches  on  the  ground; 
I  foot  represents  50  feet;  i  yard,  50  yards;  and,  in  fact, 
I  unit  represents  50  units.  It  is  immaterial  what 
the  unit  may  be.  It  is  weU  to  remember  that  the 
majority  of  maps  are  based  on  the  inches  to  the  mile 
scale,  and  if  a  pilot  once  trains  his  eye  to  readily 
recognize  the  length  of  an  inch  on  paper  he  will 
readily  estimate  the  distance  between  any  two  points 
on  a  map  with  considerable  accuracy.  Maps  of  a 
foreign  and  colonial  origin  are,  however,  generally 
constructed  so  that  the  denominator  is  a  multiple 
of  ten.  For  an  example  the  scale  adopted  for  military 
maps  of  South  Africa  is  Ybis^HTd)  and  the  scales  used 
for  the  German  maps  are: 

Ts.TRTo  for  roads  and  rivers.  This  scale  is  rather 
more  than  two  and  a  half  inches  to  a  mile. 

ra.iiyo-  This  scale  is  used  for  positions,  and  is 
somewhat  more  than  five  inches  to  a  mile,  but  for 

38 


MAP-READING 

tracts   of  country  tuo^^oUi  less  than  one  inch  to  a 
mile,  is  used. 

Map-reading  Definitions 

Basin.  This  term  is  used  to  describe  a  small  area 
of  level  ground  surrounded,  or  nearly  surrounded,  by 
hills,  and  also  to  describe  a  district  drained  by  a 
river  and  its  tributaries,  as  the  "Basin  of  the  Thames." 

Crest.  The  top  of  a  hill  or  mountain. 

Contour.  An  imaginary  line  along  the  surface 
of  the  ground  at  the  same  height  above  mean  sea- 
level  throughout  its  length. 

Dune.  A  hill  or  ridge  of  sand  formed  by  the  wind. 

Escarpment.     An  extended  line  of  cHfIs  or  bluffs. 

Gorge.     A  rugged  and  deep  ravine. 

Hachures.  Hachuring  of  a  vertical  nature  is  the 
conventional  method  of  representing  hill  features  by 
shading  in  short  disconnected  lines  drawn  directly 
down  slopes  in  the  direction  of  the  flow  of  water  on 
the  slopes. 

Knoll.     A  low  detached  hill. 

Meridian  or  North  Line.  A  true  north-and- 
south  Une. 

Magnetic  Meridian.  A  magnetic  north-and-south 
line. 

39 


THE  EYES  OF  THE  ARMY  AND  NAVY 

Pass.  A  track  over  a  mountain  range.  Usually 
a  depression  in  the  range. 

Plateau.    An  elevated  plain. 

Plotting.  The  process  of  taking  notes  and 
sketches  of  observations  and  measurements. 

Salient  or  Spur.  A  projection  from  the  side  of 
a  hill  or  mountain  running  out  of  the  main  feature. 

Setting  or  Orienting.  A  person  is  said  to  set  a 
map  when  placing  a  map  or  plan  so  that  the  north- 
and-south  line  points  north  and  south. 

Underfeature.  a  minor  feature;  an  offspring 
of  a  main  feature. 

Undulating  Ground.  Ground  which  alternately 
rises  and  falls  gradually. 

Watercourse.  The  line  defining  the  course  of 
water.  The  lowest  part  of  a  valley,  whether  occu- 
pied by  water  or  not. 

Watershed.  A  ridge  of  land  separating  two  draiit- 
age  basins.  A  summit  of  land  from  which  water 
divides  or  flows  in  two  directions.  This  term  does 
not  necessarily  include  the  highest  point  of  a  range 
of  mountains  or  hills. 

There  are  many  other  terms,  such  as  hill,  river, 
mountain,  island,  cliff,  and  ravine,  which  I  do  not 
think  it  necessary  to  define. 

40 


MAP-READING 


with  TowBr 


''/N 


Church  or  Chapet 


with  Spire 


without  To¥ver 
or  Spire 


Windmill 


fioad  enc/oaed  by  hedge,  fknce.  ditch 
orobstQcfe  of  any  kind. 


Embankment 


Villages 

under  4-' to  I  Mile- 


Cutting 


Wootf 


For^^ 


ABBREVIATIONS        Entrenchntents 

P."- .....Post  OfTice 

T Telegraph    «         footpath    ' 

S.R  —  Sign  Post 


CONVENTIONAL  SIGNS  ADOPTED  ON  SERVICE  MAPS  AND  FIELD  SKETCHES 


41 


THE  EYES  OF  THE  ARMY  AND  NAVY 

Conventional  Signs  Adopted  on  Service  Maps  and  Field 

Sketches 

Railways  are  indicated  by  a  heavy  line  and  roads 
by  a  double  line.  On  all  maps  and  field  sketches  the 
north  line  and  magnetic  north  line  are  almost  in- 
variably indicated,  and  in  making  field  sketches  and 
notes  on  observations  the  point  should  be  observed 
and  marked  on  the  sketch. 


IV 

CROSS-COUNTRY   FLYING 

ON  most  naval  and  military  aeronautical  services 
special  rules  and  regulations  are  laid  down  and 
must  be  carried  out  before  a  pilot  is  allowed  to  under- 
take a  cross-country  flight,  but  from  experience  I 
advise  the  student-pilot  to  use  common  sense  and  to 
memorize  a  few  common-sense  rules.  Before  start- 
ing on  a  cross-country  flight  always  assure  yourself 
that  your  machine  is  in  perfect  condition.  Have  the 
engine  tested  and  personally  examine  the  controls, 
control  wires,  landing-wires,  chassis,  and  the  ma- 
chine in  general.  Insure  that  the  tires  are  sufficiently 
inflated  and  that  the  dust-caps  are  screwed  on. 
Tank-caps  should  also  be  securely  screwed  down. 
Until  you  know  your  mechanics  are  reliable  always 
make  certain  yourself  that  you  have  a  petrol  and  oil 
supply  for  the  journey.  A  careless  mechanic  may  be 
the  cause  of  a  forced  landing,  and  a  landing  of  this 
nature  may  cause  damage  to  the  machine.  Map  out 
your  course  and  always  take  a  map  or  sketch  of  the 

43 


THE  EYES  OF  THE  ARMY  AND  NAVY 

country  that  you  intend  passing  over.  Make  notes 
of  prominent  landmarks.  The  most  difficult  country'- 
over  which  to  navigate  is  where  the  ground  is  covered 
with  a  network  of  small  roads  and  dotted  with  ham- 
lets and  small  villages.  Roads  do  not  make  good 
landmarks,  as  at  a  height  they  all  look  alike. 

A  good  way  to  identify  a  small  village  is  by  the 
position  of  the  church  with  reference  to  the  roads. 
On  large  maps  streams  are  usually  much  more  con- 
spicuous on  the  map  than  on  the  ground. 

Railways  are  always  very  good  landmarks,  and 
as  a  rule  are  very  conspicuous.  Towers,  windmills, 
church  spires,  and  the  like  are  as  a  rule  not  very 
conspicuous  unless  flying  low. 

Woods  are  usually  very  accurately  marked  on  ser- 
vice maps  and  are  seen  very  easily  from  above. 

When  traveling  directly  into  the  eye  of  the  sun 
a  slight  haze  is  liable  to  obliterate  many  landmarks, 
but  on  such  occasions  water  can  usually  be  detected 
many  miles  away. 

If  the  journey  is  to  be  a  long  one  it  is  advisable  to 
obtain  a  weather  report  from  the  place  of  destination ; 
otherwise  a  pilot  may  run  into  a  mist  or  fog  when 
nearing  his  destination  and  disastrous  results  may 
follow. 

Always  "take  off"  and  land  head  to  wind,  and  while 
flying  keep  a  sharp  lookout  for  other  aircraft.     If  a 

44 


CROSS-COUNTRY    FLYING 

pilot  should  encounter  other  aircraft  he  should  not 
leave  it  to  the  pilot  of  the  other  machine  to  keep 
clear  of  his  own  machine,  no  matter  how  well  he  is 
acquainted  with  the  good  qualities  of  the  other  pilot ; 
on  the  contrary,  he  should  assume  that  the  other 
pilot  is  a  "blockhead"  and  doing  his  best  to  collide. 
If  pilots  follow  this  principle  collisions  in  the  air  will 
be  greatly  eliminated. 

The  direction  of  the  wind  can  be  ascertained  by 
the  direction  of  the  smoke  from  factory  smoke- 
stacks or  house-chimneys,  but  never  imder  any  cir- 
cumstances consider  the  direction  of  smoke  from  a 
moving  train  or  steamboat.  As  you  fly  along,  fre- 
quently consider  how  the  present  wind  wiU  affect 
j'-our  return  journey. 

If  a  pilot  makes  a  forced  landing,  the  care  of  his 
machine  and  the  immediate  resumption  of  his  jour- 
ney should  be  his  first  thoughts.  If  repairs  are  likely 
to  take  considerable  time  it  is  advisable  to  get  the 
machine  under  cover  and  well  guarded,  as  inquisitive 
onlookers,  while  not  intending  to  damage  a  machine, 
have  frequently  been  the  cause  of  further  delay  by 
petty  meddling.  If  a  pilot  is  unable  to  obtain  shelter 
for  the  machine  it  is  advisable  to  lash  the  machine 
down  and  cover  the  engine. 

It  is  advisable  after  every  flight  to  report  the 
condition  of  the  engine  and  the  machine  in  general 

45 


THE  EYES  OF  THE  ARMY  AND  NAVY 

to  the  engineer  rating  and  the  carpenter  rating  in 
charge  of  the  respective  machine. 

In  cross-country  flying  the  chief  danger  is  that  the 
engine  will  fail  when  the  aeroplane  is  over  ground  on 
which  it  is  impossible  to  land.  When  the  engine 
"gives  up  the  ghost"  the  machine  must  come  down 
somewhere  inside  a  circle  whose  radius  is  about 
equal  to  five  times  the  height  of  the  aeroplane  above 
the  ground.  If  an  aeroplane  is  flying  at  a  height  of 
one  mile  the  pilot  will  have  an  area  of  about  60 
square  miles  in  which  to  choose  a  landing-ground, 
while  at  a  height  of  2,000  feet  on  a  calm  day  the 
machine  has  less  than  10  square  miles  to  choose 
from.  In  England  it  is  almost  always  possible  to 
choose  a  favorable  landing-place  in  a  circle  containing 
60  square  miles,  but  it  is  frequently  impossible  to  do 
so  in  an  area  of  10  square  miles.  For  this  reason 
cross-coimtry  trips  should  never  be  undertaken  when 
clouds  are  at  a  low  altitude. 

War  Flight 

If  a  pilot  is  about  to  leave  on  a  bomb-dropping 
expedition  he  should  personally  examine  all  bombs. 
The  wind-vanes  should  work  freely  and  the  safety 
pins  should  be  removed.  The  dropping-gear  should 
be  tested  by  having  a  man  stand  under  the  bomb- 

46 


CROSS-COUNTRY    FLYING 

frame  and  catch  the  bomb  when  the  bomb  is  released 
by  movement  of  the  releasing-lever.  The  machine- 
gun  should  be  tested  by  firing  from  twenty  to  thirty 
rounds  a  few  degrees  from  the  vertical.  If  the  ma- 
chine is  equipped  with  a  wireless  outfit,  see  that  the 
instruments  are  in  working  order. 

Hints  for  Beginners 

Always  examine  machine  and  test  controls  before 
every  flight.  Have  the  engine  running  to  your  satis- 
faction before  going  up.  Do  not  be  satisfied  with 
another  person's  opinion.  You  are  to  pilot  the  ma- 
chine; be  satisfied  with  the  condition  of  the  engine 
and  the  machine  in  general.  Strap  yourself  in.  See 
that  no  other  machines  are  preparing  to  land,  and  be 
sure  that  your  control  lever,  or  control  wheel,  is  at 
the  neutral  position  before  "taking  off,"  and  always 
"take  off"  head  to  wind. 

Do  not  attempt  to  turn  before  sufficient  height  has 
been  reached.  A  beginner  should  never  turn  unless 
at  a  height  of  500  feet. 

Always  put  "nose  down"  slightly  before  turning 
and  put  on  the  correct  amount  of  bank. 

Do  not  fly  by  the  instruments.  Learn  to  fly  by 
"feel,"  and  only  refer  to  the  instruments  for  con- 
firmation. 

47 


THE  EYES  OF  THE  ARMY  AND  NAVY 

At  all  times  keep  a  sharp  lookout  for  other  aircraft, 
and  conform  to  the  "Rules  of  the  Air"  posted  up  at 
all  air  stations. 

If  side-slipping  occurs,  always  turn  in  the  direction 
in  which  the  machine  is  slipping  and  put  "nose  down  " 
sHghtly  until  perfect  control  is  regained.  A  good 
method  to  adopt  to  ascertain  whether  machine  is 
slipping  is  to  tie  a  piece  of  string  from  the  center 
forward  struts,  and  if  placed  correctly  the  piece  of  string 
should  blow  straight  back.  If  it  blows  in  a  direction 
to  the  right  of  a  pilot,  it  indicates  that  from  the  left 
side  of  the  machine  there  is  a  greater  pressure;  and 
if  the  string  blows  to  the  left  of  the  pilot,  it  indicates 
a  greater  pressure  from  the  right  side  of  the  machine. 
(Figs.  19,  20,  and  21.) 

A  beginner  should  never  attempt  to  "stunt"  under 
an  altitude  of  5,000  feet.  If  any  difficulty  with  en- 
gine or  control  is  experienced  while  in  the  air,  come 
down. 

If  volplaning  from  a  great  height,  switch  on  your 
engine  for  a  few  seconds  every  1,000  feet.  This  will 
clear  the  cylinders  of  surplus  petrol  and  oil;  if  this 
practice  is  carried  out,  possibility  of  the  engine 
"choking"  will  be  practically  eliminated. 

Before  attempting  to  land,  make  sure  that  the 
landing-field  is  clear,  and  land  head  to  wind.  It  is 
better  to  get  into  the  habit  of  "undershooting"  the 

48 


CROSS-COUNTRY    FLYING 

landing-field  than  ** overshooting."  In  the  first  case 
a  pilot  can  always  switch  off  for  a  few  seconds  (pro- 
vided the  engine  is  in  perfect  order);   whereas,  if  he 


STRING  BLOWING 
STRAIGHT  BACK,  NO 
SIDE-SLIPPING 


STRING  BLOWING 
TO  RIGHT  OF  PILOT, 
GREATER  PRESSURE 
FROM  LEFT  INDICAT- 
ING SIDE-SLIPPING 
TO  LEFT 

(W)  Indicates  greater  pressure. 
(Z)  Direction  of  side-slipping. 
(Y)  Direction  of  string. 
(X)  Pilot's  seat. 
(V)  Forward  center  struts. 


STRING  BLOWING 
TO  LEFT  OF  PILOT, 
GREATER  PRESSURE 
FROM  RIGHT  INDI- 
CATING SIDE-SLIP- 
PING TO  RIGHT 


"overshoots"  the  landing-field,  he  is  obliged  to  make 
another  circuit. 

A  "flying"  log-book  should  be  kept  by  all  pilots, 
and  columns  should  be  correctly  filled  in.  Under  a 
colimm  headed  "Wind"  the  direction  and  velocity  of 
the  wind  should  be  stated.    Under  a  column  headed 

49 


THE  EYES  OF  THE  ARMY  AND  NAVY 

"Remarks"  against  each  flight  a  small  diary  of  the 
record  of  the  flight  should  be  given. 


Method  of  Marking  Landing-grounds 

The  majority  of  landing-grounds  have  a  T  for  in- 
dicating the  direction  of  the  wind.    This  T  consists  of 


Direction  in  which  a 
pilot  should  land 


fig. 22 

strips  of  linen  tacked  on  to  a  framework  of  wood  and 
is  generally  placed  in  the  center  of  the  landing-field 
with  the  head  of  the  T  facing  directly  to  the  direction 
of  the  wind.  The  position  of  the  T  should  be  changed 
with  any  slight  change  of  the  wind.     (Fig.  22.) 


V 

CHARTS 

ALTHOUGH  it  is  not  imperative  that  a  pilot 
IX  should  know  the  difference  of  buoys,  their 
meanings,  the  abbreviations  used  in  the  Admiralty 
list  of  lights,  and  the  definitions  of  the  characteristic 
phrases,  it  is  advisable  to  describe  the  most  important. 
In  some  examinations  queries  on  the  subject  crop 
up,  and  to  seaplane  pilots  the  information  may  prove 
beneficial  in  the  days  of  the  sea  patrol. 

Starboard-hand  Buoys 

By  the  term  starboard  hand  is  meant  that  side 
which  will  be  on  the  right  hand,  when  going  with  the 
main  stream  or  flood  tide,  or  when  entering  a  harbor, 
river,  or  estuary  from  seaward. 

The  term  port  hand  indicates  that  side  which  will 
be  on  the  left  hand  under  the  same  circumstances. 
(Fig.  23.) 

Starboard-hand  buoys  mark  the  starboard  side  of 

SI 


THE  EYES  OF  THE  ARMY  AND  NAVY 

a  channel  as  defined  above.  They  are  conical  in 
shape  and  are  painted  one  color;  in  England,  red  or 
black;  in  Scotland  and  Ireland,  red  only.  Quite 
often  starboard-hand  buoys  are  surmounted  by  a 
top  mark  in  order  that  they  may  be  distinguished 
readily.  This  top  mark  consists  of  a  staff  and  globe, 
as  shown  in  Fig.  23. 

Port -hand  Buoys 

Port-hand  buoys,  buoys  that  indicate  the  port  side 
of  a  channel  as  defined  above,  show  a  flat  surface 
above  the  water  and  are  termed  can  buoys.  In 
England  they  are  painted  red  and  white  or  black  and 
white,  showing  cheques  or  vertical  stripes.  (Figs.  24 
and  25.) 

In  Scotland  and  Ireland  they  are  painted  black. 
The  distinguishing  top  mark  for  this  type  of  buoy 
consists  of  a  staff  and  cage. 

Middle-ground  Buoys 

What   is   known    as   middle   ground,    which   is    a 
shoal  with  a  channel  on  either  side  of  it,  has  its  ends 
marked  by  buoys  which  show  a  domed  top  above 
water  and  are  known  as  spherical  buoys  and  are  \ 
colored  with  horizontal  stripes.    A  buoy  of  this  type, 

52 


CHARTS 

surmounted  with  a  staff  and  diamond  (see  Fig.  26), 
indicates  the  outer  end  of  the  middle  ground;  and  a 
spherical  buoy  surmounted  with  a  staff  and  triangle 
marks  the  inner  end. 


Telegraph  Buoys 

A  telegraph  buoy  is  generally  placed  over  a  tele- 
graph cable.     It  is  conical  in  shape  and  usually  has 


F"ig.23 


BLACK 


Fig.  24 


»■    I 


I    ■    ■ 


RED  AND    WHITE 
CHEQUERS 


BLACK   AND   WHITE 
VERTICAL    STRIPES 


BLACK  AND   WHITE 
HORIZONTAL    STRIPES 


S3 


THE  EYES  OF  THE  ARMY  AND  NAVY 

the  word  "Telegraph"  painted  on.  This  buoy  is 
painted  green.  What  is  known  as  a  wreck  buoy  is 
similar  to  a  telegraph  buoy  and  has  the  word  "Wreck" 
painted  on.    This  buoy  is  also  painted  green. 

Spoilt-ground  Buoys 

A  spoilt-ground  buoy,  used  to  indicate  ground  used 
by  dredges,  is  usually  conical  in  shape  and  painted 
yellow  and  green  vertical  stripes. 

Abbreviations 

The  following  abbreviations  generally  shown  below 
buoys  on  a  chart  indicate  the  characteristics: 

R Red 

B.,  Blk Black 

G Green 

Cheque Chequered 

H.  S Horizontal 

W White 

Y Yellow 

V.  S Vertical  stripes 

Lights 

Lights  may  be  divided  into  two  classes,  namely: 
Lights  whose  colors  do  not  alter  throughout  the 

54 


CHARTS 

whole  system  of  changes,  and  lights  which  alter  in 
color. 

The    following    abbreviations    and    characteristic 
phases  should  be  committed  to  memory: 


Lights  Whose 

Colors  Do  Not 

Change 

Characteristic  Phases 

Lights  Which 
Alter  in 
Color 

F.  Fixed 

A  continuous,  steady  light 

Alt.  Alternating 

Fl.  Flashing 

(A)  Showing  a  single  flash  at 

Alt.  Fl. 

regular  intervals,  the  du- 

Alternating 

ration  of  light  being  al- 

flashing 

ways  less  than  that  of 

darkness 

(B)  A   steady   light   with   a 

total   eclipse  at  regular 

intervals;  the  duration  of 

light   being   always   less 

than  that  of  darkness 

Gp.  Fl. 

Showing  a  group  of  two  or 

Alt.  Gp.  Fl. 

Group 

more  flashes  at  regular  inter- 

Alternating 

flashing 

vals 

group  flashing 

Occ.  Occulting 

A  steady  light  with  a  sudden 

Alt.  Occ. 

and  total  eclipse  at  regular 

Alternating 

intervals;     the    duration    of 

occulting 

darkness   being   always   less 

than,   or  equal   to,   ths^t  of 

light 

Gp.  Occ.  A  steady  light  with  a  group  of 

Group  two  or  more  sudden  eclipses 

occulting  at  regular  intervals 

55 


Alt.  Gp.  Occ. 
Alternating 
group 
occulting 


THE  EYES  OF  THE  ARMY  AND  NAVY 


Lights  Whose 

Colors  No  Not 

Change 


Characteristic  Phases 


Lights  Which 
Alter  in 
Color 


F.  Fl. 
Fixed  and 
flashing 


F.  Gp.  Fl. 

Fixed  and 

group 

flashing 


Rev.  Revolving 


A  fixed  Ught  varied  by  a 
single  flash  of  relatively 
greater  brilliancy  at  regular 
intervals.  The  flash  may,  or 
may  not,  be  preceded  and 
followed  by  an  eclipse 
A  fixed  light,  varied  at  regular 
intervals  by  a  group  of  two  or 
more  flashes  of  relatively 
greater  brilUancy.  The  group 
may,  or  may  not,  be  preceded 
and  followed  by  an  eclipse 
A  light  gradually  increasing 
to  full  briUiancy,  then  de- 
creasing to  eclipse 


Alt.  F.  Fl. 
Alternating 
fixed  and 
flashing 


Alt.  F.  Gp.  Fl. 
Alternating 
fixed  and 
group  flashing 


Alt.  Rev. 
Alternating 
revolving 


VI         * 

METEOROLOGY 

IT  cannot  be  too  strongly  impressed  upon  pilots 
of  aircraft  that  the  impending  weather  conditions 
are  of  the  greatest  importance  and  a  pilot  should 
know  how  to  study  a  weather  chart  and  have  a 
knowledge  of  forecasting  weather. 

Aeroplane  Weather 

Calm,  clear  weather  with  little  or  no  wind  is  the 
most  suitable  for  aeroplanes.  The  only  conditions 
which  make  it  impossible  for  a  good  pilot  to  fly  a 
modern  aeroplane  are  a  strong  gale  or  fog.  Such 
conditions  prevent  useful  work  from  being  carried 
out  by  aeroplanes.  Military  and  civilian  flying  is 
affected  by  the  weather  in  quite  different  ways. 
When  a  machine  is  tested  with  a  view  to  finding  the 
rate  of  climb,  the  maximum  speed  when  flying  level, 
the  best  landing  speed,  and  the  other  aerodynamical 
qualities,  it  is  usually  necessary  to  wait  for  a  calm 

57 


THE  EYES  OF  THE  ARMY  AND  NAVY 

day,  when  eddies,  or  large  ascending  or  descending 
currents,  or  other  conditions  prejudicial  to  accurate 
testing,  are  unlikely  to  occur. 

When  flying  under  war  necessities  eddied  and 
vertical  currents  are  almost  immaterial,  provided  they 
are  not  so  violent  as  to  impede  observations.  Low 
clouds  make  observations  over  the  enemy's  lines  al- 
most impossible,  owing  to  the  accuracy  of  modem 
anti-aircraft  guns.  Detached  clouds  often  impede 
but  do  not  put  a  stop  to  reconnaissance. 

A  ground  haze,  very  evident  on  calm  days,  fre- 
quently makes  it  impossible  to  carry  out  useful  re- 
connaissance, and  on  these  occasions  the  direction 
of  the  sun  is  an  important  factor.  At  a  time  of 
day  when  the  sun  is  behind  the  enemy's  lines  it 
is  impossible  to  observe  enemy  operations  except 
from  behind  their  own  lines,  where  the  sun  need  not 
be  faced. 

In  England  easterly  and  northeasterly  winds  are 
uncomfortable  for  flying  because  the  "bumps"  are 
more  violent  and  extend  to  a  greater  height  in  winds 
from  the  above  directions  than  in  winds  from  the 
west.  In  North  America  winds  from  the  east  and 
southeast  are  the  most  favorable.  Early  morning 
and  evening  are  the  best  times  for  school  and  civilian 
flying.  At  these  periods  of  the  day  the  air  is  much 
calmer  than  at  other  times. 

S8 


METEOROLOGY 
The  Atmosphere 

The  atmosphere  is  a  gaseous  body  which  sur- 
rounds the  earth.  It  is  elastic,  very  sensitive  to  the 
action  of  heat,  and  is  necessarily  much  denser  in  the 
vicinity  of  the  earth's  surface  than  above.  From  ob- 
servations it  has  been  discovered  that  at  a  height  of 
six  miles  the  atmosphere  is  so  rarefied  that  great 
difficulty  is  found  in  breathing. 

Composition  of  Atmosphere 

The  composition  of  the  atmosphere,  for  all  prac- 
tical aeronautical  purposes,  may  be  considered  as 
follows : 

Nitrogen 79  per  cent. 

Hydrogen 20  per  cent. 

Argon I  per  cent. 

These   constituents   diminish   as   height   is   attained 
and  other  gases  take  their  places. 

Atmospheric  Pressure 

Pressure  of  the  atmosphere  is  the  weight  of  the 
air  pressing  down  just  as  the  weight  of  water  in  a 
pond  exerts  a  certain  pressure  on  the  bottom.  The 
atmospheric  pressure  at  the  surface  of  the  earth  is 

59 


THE  EYES  OF  THE  ARMY  AND  NAVY 

not  constant,  but  varies  from  day  to  day.  This 
pressure  is  measured  by  means  of  an  instrument 
called  a  barometer,  by  which  the  pressure  is  measured 
by  the  height,  in  inches,  of  a  column  of  mercury 
necessary  to  balance  it.  The  average  pressure  of  the 
atmosphere  at  the  surface  of  the  earth  is  29.8  inches. 
In  the  British  Isles,  at  a  certain  time  each  day  the 
atmospheric  pressures  are  taken  at  a  number  of 
places  and  flashed  to  a  head  meteorological  office,  and 
later  what  is  known  as  a  synoptic  chart  or  weather 
chart  is  made  out.  The  places  which  register  the 
same  barometric  pressure  are  joined  by  a  line,  and 
this  line  is  known  as  an  isobar.  (These  isobars  may 
be  likened  to  contour  lines  on  an  ordinary  map.  Cer- 
tain areas  will  have  high  pressure,  while  other  areas 
will  have  low  pressures. 

In  addition  to  the  atmospheric  pressures  the  direc- 
tion and  force  of  the  wind  and  the  Fahrenheit  tem- 
perature will  be  registered  at  each  observation  sta- 
tion and  marked  on  the  synoptic  chart.  (In  the  lowest 
strata  the  height  of  the  mercury  column  decreases 
approximately  one-tenth  of  an  inch  for  every  ninety 
feet  above  sea-level.) 

Measure  of  Pressure 

Barometric  pressure  is  now  measured  in  pressure 
units  as  well  as  in  inches  of  mercury.     Since  the 

60 


METEOROLOGY 

study  of  meteorology  in  connection  with  aircraft, 
this  method  has  been  adopted,  as  the  measuring  of 
pressure  by  inches  of  mercury  only  was  very  unsatis- 
factory for  accuracy.  The  centimetre  gram  second 
system,  better  known  as  the  "C.  G.  S."  system,  is 
used.  The  absolute  unit  of  pressure  on  this  system 
is  the  dyne  per  square  centimetre.  As  this  unit  is  an 
exceedingly  small  one,  it  was  suggested  by  the  meteoro- 
logical authorities  that  a  practical  unit  one  million 
times  greater  be  used.  This  unit,  the  megadyne 
per  square  centimetre,  is  called  a  '.'bar."  In  daily 
weather  reports  the  centibar  and  the  millibar,  respec- 
tively the  hundredth  and  the  thousandth  part  of  a 
bar,  have  been  adopted  as  working  units. 

Approximate  Relation 

The  approximate  relation  between  the  millibars 
and  inches  of  mercury  is  given  below,  and  the  list 
covers  all  that  is  required  to  be  known  by  the  pilot 
for  practical  purposes. 


AT 

32°  F. 

AND 

LATITUDE 

45°: 

Ins. 

Milli- 
bars. 

Ins. 

MUli- 
bars. 

Ins. 

Milli- 
bars. 

Ins. 

MUli- 
bars. 

Ins. 

Milli- 
bars. 

Ins. 

Milli- 
bars. 

28.00 

28.10 

28.20 
28.30 
28.40 

948.2 
95 1.6 
9S4.9 
958.3 
961.7 

28.50 
28.60 
28.70 
28.80 
28.90 

965.1 
968.5 
971.9 
975-3 
978.6 

29.00 
29.10 
29.20 
29.30 
29.40 

982.0 

985-4 
988.8 
992.2 
995.6 

29.50 
29.60 
29.70 
29.80 
29.90 

999.0 
1,002.4 
1,005.7 
1,009.1 
1,012.5 

30.00 
30.10 
30.20 
30.30 
30.40 

1,015.9 
1,019.3 
1,022.7 
1,026.1 
1,029.4 

30.50 
30.60 
30.70 
30.80 
30.t>o 

1,032.8 
1,036.2 
1 ,039.6 
1,043.0 
1 ,046.4 

61 


THE  EYES  OF  THE  ARMY  AND  NAVY 

High  and  Low  Pressure  Regions 

A  pressure  under  29.8  inches  of  mercury  or  approxi- 
mately 1,010  millibars  represents  a  low-pressure  re- 
gion, and  above  that  reading  an  area  is  known  as  a 
high-pressure  region.  The  former  is  known  as  a 
cyclone  or  cyclonic  depression  and  the  latter  an  anti- 
cyclone or  anti-cyclonic  region.  From  experience  it 
has  been  proved  that  anti-cyclonic  conditions  are,  in 
general,  more  favorable  for  flying  than  conditions  of  a 
cyclonic  nature.  The  distribution  of  pressure  governs 
the  winds.  In  a  region  where  the  pressure  is  changing 
rapidly  the  wind  will  be  strong,  and  in  a  region  where 
the  pressure  is  more  or  less  uniform  the  wind  will 
be  light. 

Cyclone  or  Low-pressure  Region 

The  weather  to  be  expected  in  a  cyclone  or  low- 
pressure  region  is  shown  in  Fig.  27,  and  the  small 
arrows  indicate  the  direction  of  the  wind.  The  large 
arrow  passing  through  the  center  of  the  figure  in- 
dicates the  direction  of  the  depression.  As  the  cy- 
clone approaches  an  observer  the  barometer  falls, 
and  this  continues  until  the  center  of  the  region  has 
passed  and  then  the  barometer  begins  to  rise.  A 
line  through  the  center  of  the  cyclone  and  perpendic- 
ular to  its  path  is  known  as  the  "trough"  of  the 

62 


METEOROLOGY 

cyclone  and  is  associated  with  a  squall  or  heavy 
shower.  This  is  known  as  the  clearing  shower, 
as  it  generally  indicates  the  approach  of  fine  weather. 
As  a  rule,  cyclones  move  in  a  direction  from  south- 


Cumuluj 

Blue  Sky 

•^  \Nindy  Cirrus 


Fig.  27 

southwest  to  east-northeast.  The  usual  path  lies 
rather  to  the  north  of  Scotland,  so  that  the  British 
Isles  generally  come  in  for  the  weather  expected  in  the 
southern  part  of  the  cyclone.  When  the  influence  of 
a  cyclone  is  evident  the  direction  of  the  wind  is 
south  or  southeast;  the  barometer  begins  to  fall  and 
light  wisps  of  cirrus  clouds  appear.    As  the  cyclone 

63 


THE  EYES  OF  THE  ARMY  AND  NAVY 

approaches  the  clouds  thicken,  the  wind  changes  to 
the  southwest,  and  rain  begins  to  fall.  This  continues 
until  the  "trough"  passes.  The  barometer  then  be- 
gins to  rise;  frequently  in  a  sudden  squall,  the  wind 
changes  to  the  west  or  northwest.  The  weather  then 
clears  and  after  a  few  showers  becomes  fine  and  a 
northwest  wind  usually  prevails. 

Line  Squalls 


It  has  been  stated  that  when  a  trough  of  a  cyclone 
passes  there  is  usually  a  heavy  squall  and  a  change  in 


/^' 

^ 

Cumulus 

Cloudless 

s^O 

( 

'V 

\Frcst 

Calm      ^^\     ,„  ^ 

.^X  30  2 

RAD/AriON^\ 

M!u  \ 

Cold  Air           Hot  Sun          1 

WEATHER         Dt^j 

\ 

\ 

Stratus     \. 

Calm       ^^^y^ 

J 

Sometimes 

Bitter  E  Vimds 
Black  Skj  in  Winter  ^^< 

1 

Fig.  28 

64 


METEOROLOGY 

the  direction  of  the  wind.  Squalls  of  this  kind  are 
known  as  line  squalls  and  are  generally  very  sudden 
and  violent.  This  sudden  change  in  the  direction 
and  velocity  of  the  wind  makes  these  squalls  very 
dangerous  to  aircraft.  When  a  trough  of  a  cyclone 
passes  they  are  to  be  expected  and  also  when  an  ir- 
regularity in  the  isobars  on  the  edge  of  a  cyclone 
known  as  a  "secondary  depression"  passes.  They 
sometimes  occur  when  there  is  no  such  warning  of 
their  approach .     (Fig .  2  8 . ) 

Anti-cyclone 

The  weather  to  be  expected  in  an  anti-cyclone  or 
high-pressure  region  is  shown  in  Fig.  27,  and  it  will 
be  observed  that  the  conditions  are  almost  the  reverse 
to  those  in  a  cyclonic  depression.  The  winds  are 
usually  light  and  blow  round  the  center  in  a  clock- 
wise direction.  Although  the  sky  may  in  some  cases 
be  cloudy,  the  weather  is  generally  fine.  In  a  region  of 
this  nature  mist  or  fog  very  frequently  occurs  in  the 
early  morning.  An  anti-cyclone  has  no  general 
direction  of  motion  and  may  move  in  any  direction 
and  is  frequently  stationary  for  days. 

Wind 

Wind  is  air  in  motion.  It  is  not  necessary  for  the 
pilot  to  study  the  cause  of  the  winds  and  the  reason  of 

65 


THE  EYES  OF  THE  ARMY  AND  NAVY 

their  distribution.  In  most  cases  the  air  flows  from 
an  area  of  relatively  high  pressure  to  a  region  of 
relatively  low  pressure.  The  velocity  of  the  wind  is 
governed  by  the  relative  pressure  in  the  adjoining 
areas  and  is  determined  by  the  barometer  gradient. 
A  scale  known  as  Beaufort's  Scale  is  used  for  the  pur- 
poses of  reference  and  classifies  the  various  velocities 
of  the  wind. 

BEAUFORT   SCALE 

Beaufort  Nautical 

Force  Miles  per  Description  of  Wind 

Number  Hour 


j    Less     I 
( than  I  ) 


.Calm 


1  1-3  Light  air 

2  4-6  SUght  breezes 

3  7-10  Gentle  breezes 

4  1 1-16  Moderate  breezes 

5  17-21  Fresh  breezes 

6  22-27  Strong  breezes 

7  28-33  High  wind 

8  34-40  Gales 

9 41-47  Strong  gales 

10 48-55  Whole  gale 

11  56-65  Storm 

12  Above  65 Hurricane 

Veering  of  Wind 

As  height  is  attained  the  velocity  of  the  wind  in- 
creases in  strength,  and  in  the  northern  hemisphere 

66 


METEOROLOGY 

it  is  usually  said  to  "veer,"  which  indicates  that  it 
goes  round  in  a  clockwise  direction.  This  increase  in 
velocity  continues  to  a  height  of  from  2,000  to  3,000 


2500 


Wind   Velocity  in   Miles  per  Hour 
10  20  30  40 


2000 


1500 


1000 


500 


» 

,._ 

/ 

/ 

Ground  Lev* 

>l 

/ 

Sea  Level 

Fig.  29 


RELATION   OF    WIND   VELOCITY   TO   HEIGHT 


feet,  after  which  it  sometimes  increases  and  some- 
times decreases,  but  on  the  average  remains  nearly 
constant.     The  following  scales  are  used  when  work- 

67 


THE  EYES  OF  THE  ARMY  AND  NAVY 

ing  out  problems  in  which  the  upper  wind  is  to  be 

considered : 

At  i,ooo  feet  the  wind  veers  lo  degrees. 
At  2,000  feet  the  wind  veers  15  degrees. 
At  3,000  feet  the  wind  veers  20  degrees. 
Above  this  height  the  wind  remains  practically  constant. 

Increase  in  Velocity  Relative  to  Height 

At  1,000  feet  the  velocity  of  the  wind  increases  to  one  and  a 
half  times  its  own  velocity. 

At  2,000  feet  the  velocity  of  the  wind  increases  to  twice  its 
own  velocity. 

Above  2,000  feet  there  is  practically  no  increase. 

The  Gradient  Wind 

The  gradient  wind  is  a  theoretical  wind  calculated 
from  the  pressure  gradient  and  the  deflecting  force 
due  to  the  earth's  rotation.  If  V  is  speed  of  gradient 
wind  in  knots  and  D  the  distance  between  the  isobars 
on  either  side  of  a  place  considered,  then  V  =  '^ 

Isobar 


t 
120  Miles 


29.83' 


Isobar 


29.98" 


Fig.  30 


Velocity  =   i^r  ~  29  knots  per  hour  (approximately). 
68 


5      -•  METEOROLOGY 

Gusts  or  "Bumps" 

Gusts,  better  known  as  "bumps,"  is  an  expression 
used  to  denote  a  turbulent  motion  of  the  air.  These 
bumps  are  most  conspicuous  near  the  surface  and  may- 
be attributed  to  the  effect  of  obstacles  in  the  path  of 
moving  air,  which  transform  the  uniform  motion  of 
steady  current  into  pulsating  motion  with  eddies. 
Bumps  are  sometimes  felt  at  a  height  of  5,000  feet 
and  occasionally  at  a  height  of  10,000  feet.  In  the 
former  case  they  are  sometimes  due  to  the  presence 
of  clouds.  In  the  latter  they  are  mostly  due  to  one 
current  of  air  meeting  with  another  current  moving 
in  a  different  direction. 

Wind  Eddies 


Eddies  are  very  conspicuous  in  a  strong  wind  and 
always  greater  on  the  lee  side  of  hills  and  cliffs.    On 


.g.3l 


account  of  these  wind  eddies  it  is  not  advisable  to 
land  an  aeroplane  in  the  lee  of  hills,  cliffs,  and  large 

6  69 


THE  EYES  OF  THE  ARMY  AND  NAVY 

buildings  in  a  strong  breeze.  If  a  pilot  experiences 
engine  trouble  and  a  forced  landing  is  inevitable,  lie 
should  endeavor  to  land  on  the  windward  side;  how- 
ever, if  unable  to  make  the  windward  side,  he  should 
endeavor  to  land  well  away  on  the  lee  side.     (Fig.  31.) 

Upward  Currents 

Of  these  wind  eddies  the  most  important  to  air- 
craft are  rising  currents  and  descending  currents.  A 
mass  of  air  rises  or  falls  as  its  density  decreases 
or  increases.  Warm  and  expanded  air  ascends  when 
the  surrounding  air  at  the  same  level  is  colder.  As 
the  atmosphere  is  heated  mainly  through  contact 
with  the  earth's  surface,  which  in  turn  has  been 
heated  by  the  rays  of  the  sun,  these  upward  currents 
are  very  conspicuous  during  warm,  clear  weather. 
Over  water,  currents  of  this  nature  carry  large  quanti- 
ties of  aqueous  vapor  resulting  from  the  evaporation 
of  the  water.  As  these  masses  of  air  and  aqueous 
vapor  arise  they  expand,  owing  to  the  rarefied 
state  of  the  upper  atmosphere.  These  columns  of 
air  and  vapor  lose  heat  as  height  is  attained,  and  the 
loss,  together  with  a  lower  temperature  over  the 
upper  region,  causes  the  vapor  to  be  condensed. 
This  condensed  vapor,  combined  with  the  multitudes 
of  small  dust  particles  floating  in  the  atmosphere, 

70 


METEOROLOGY 

presents  the  appearance  known  as  clouds.  From 
observation  it  has  been  discovered  that  the  rate  of 
ascent  of  these  columns  may  be  very  great,  A 
velocity  of  25  feet  per  second  has  been  known  to 
occur,  and  therefore  it  may  be  readily  seen  that  these 
vertical  velocities  are  a  source  of  danger  to  aircraft. 
If  an  aeroplane  plunges  squarely  into  a  column  of  this 
nature  it  will  cause  the  machine  to  rise;  emerging 
from  a  similar  column,  the  machine  will  drop.  Graz- 
ing a  column  with  one  wing  will  tilt  the  machine, 
and  in  the  case  of  an  airship  or  a  balloon  these  columns 
will  cause  the  airship  or  balloon  to  rise  or  fall. 

These  rising  colimms  are  encoimtered  over  flat, 
barren  country  on  clear  summer  days,  and  above 
isolated  hills  on  calm,  warm  days;  in  the  former  case 
on  account  of  the  heat  being  quickly  radiated,  and  in 
the  latter  case  on  account  of  the  sunny  side  of  the 
hills  being  warmer  than  the  surrounding  atmosphere. 
In  the  early  part  of  the  forenoon,  and  especially  over 
water  and  green  vegetation,  these  rising  currents  are 
less  frequent  than  during  the  hotter  part  of  the  day. 
Before  sunrise  and  when  the  sky  is  overcast  these  dis- 
turbances are  practically  absent. 

Descending  Currents 

Descending  currents  are  mainly  due  to  two  causes. 
In  the  upper  regions  they  are  caused  by  cold  air 

71 


THE  EYES  OF  THE  ARMY  AND  NAVY 

descending  to  take  the  place  of   rising  hot-air  cur- 
rents ;  however,  they  are  usually  not  rapid  and  do  not 


Fig.33 


cause  much  inconvenience  to  pilots.  Near  the  sur- 
face they  are  caused  by  air  flowing  up  to  or  over  a 
precipice.     (Figs.  32  and  33.) 


Wind  Layers 

Very  often  a  pilot  will  experience  wind  blowing  in 
different  directions  at  different  heights;  thus  clouds 
are  frequently  seen  moving  in  different  directions  at 
different  heights.     Helmholtz  explained  that  layers 

*  72 


METEOROLOGY 

of  air  differing  in  density  are  the  cause,  and  that  they 
glide  with  little  or  no  intermingling  one  over  the 
other,  very  much  as  air  flows  over  water  and  with  the 
same  wave-producing  effect. 

From  an  aeronautical  point  of  view  this  is  impor- 
tant, as  the  passage  from  one  layer  to  another  of  differ- 
ent speed  and  different  direction  will  cause  the  rise 
or  fall  of  a  machine;  however,  these  wind  layers 
generally  flow  somewhat  across  one  another,  so  that 
a  machine  passing  from  one  layer  to  another  will  only 
experience  a  tiu-bulent  motion  and  a  few  bumps. 

Clouds 

Under  the  heading  "Upward  Currents"  the  forma- 
tion of  clouds  by  condensation  by  cooling  was  explained. 
Condensation  by  mixing  will  also  form  clouds.  In 
this  case  it  occurs  when  a  mass  of  moist  air  en- 
counters, in  its  ascent,  another  mass  of  moist  air 
which  is  at  a  different  temperature.  Certain  types  of 
clouds  and  the  direction  in  which  they  are  moving 
indicate  the  weather  to  be  expected,  and  a  few  notes 
in  that  respect  are  given  in  the  list  of  the  different 
types  of  clouds  on  the  following  page.  Clouds  may  be 
classified  in  two  typical  forms,  cloud  sheets  and  cloud 
heaps.  The  former  may  be  divided  up  into  three 
classes  which  differ  in  appearance  and  height, 

73 


THE  EYES  OF  THE  ARMY  AND  NAVY 

The  Upper  Layer.  The  upper  layer  is  chiefly 
composed  of  the  cirrus  clouds  and  is  generally  at  a 
height  of  from  25,000  to  30,000  feet. 

The  Middle  Layer.  The  middle  layer  consists 
chiefly  of  the  alto  clouds  and  is  to  be  expected  at  a 
height  of  from  10,000  to  25,000  feet;  the  lower-layer 
clouds  are  below  9,000  feet. 

Heap  Clouds.  Clouds  of  this  form  have  consid- 
erable vertical  structure  and  their  height  is  variable. 
The  mean  height  of  the  base  is  from  4,000  to  5,000 
feet  and  the  height  of  the  top  varies  from  6,000  to 
25,000  feet. 

Cloud  Sheets 

Cirrus.  Mare's-tails ;  wisps  or  lines  of  pure  white 
clouds  with  no  shadows.  At  27,000  to  50,000  feet. 
Predict  wind  and  a  cyclonic  depression. 

Cirro-stratus.  A  thin  sheet  of  tangled  web 
structiu'e,  sometinies  covering  the  whole  sky;  watery 
sun  or  moon.  At  an  average  of  29,500  feet.  Predicts 
bad  weather. 

Cirro-cumulus.  Small  speckles  and  flocks  of 
white  clouds;  fine  ripple  clouds;  mackerel  sky.  At 
10,000  to  23,000  feet.     Denotes  fine  weather. 

Alto-cumulus.  Somewhat  similar  to  cirro-cumu- 
lus, but  the  cloud  masses  are  larger  and  show  some 
shadow.    At  10,000  to  23,000  feet. 

74 


METEOROLOGY 

Cfrro-nebula.  Similar  to  last,  but  a  veil  of 
cloud  with  no  visible  structure.  At  10,000  to 
23,000  feet. 

Alto-cumulus  Castellatus.  Turret  cloud;  alto- 
cumulus with  upper  margins  of  the  cloud  masses  de- 
veloped upward  into  miniature  cumulus,  with  hard 
upper  edges.     At  10,000  to  23,000  feet. 

Alto-stratus.  Very  like  cirro-stratus  and  cirro- 
nebula,  but  a  thicker  and  darker  cloud.  At  10,000  to 
23,000  feet. 

Strato-cumulus.  Cloud  masses  with  some  verti- 
cal structure;  rolls  or  waves  sometimes  covering  the 
whole  sky.  At  6,500  feet.  Predicts  a  change  in  the 
weather. 

Stratus.  A  uniform  layer  of  cloud  resembling  a 
fog  but  not  resting  on  the  ground.  One  hundred  to 
3,500  feet. 

Nimbus.  Shapeless  cloud  without  structure,  from 
which  falls  continuous  rain  or  snow.  At  3,000  to 
6,500  feet.     Usually  a  rain  cloud. 

Scud.  Small  shapeless  clouds  with  ragged  edges; 
sometimes  seen  without  other  cloud,  especially  in 
hilly  country;  but  more  commonly  seen  below  other 
clouds,  such  as  cumulus  and  nimbus.  At  1,000  to 
4,000  feet.     Predicts  unsettled  weather. 


75 


THE    EYES    OF   THE   ARMY   AND    NAVY 

Heap  Clouds 

Cumulus.  (Woolpack  clouds);  clouds  with  flat 
base  and  considerable  vertical  height.  Cauliflower- 
shaped  top.  At  4,500  to  6,000  feet.  These  clouds  are 
caps  of  ascension  currents  and  a  pilot  will  experience 
violent  disturbances  when  passing  through  them  or 
just  above  or  below  them. 

Cumulo-nimbus.  (Anvil-,  thunder-,  or  shower- 
cloud).  Towering  cumulus  with  the  top  brushed  out 
in  soft  wisps  or  larger  masses  (false  cirrus)  and  rain 
cloud  at  base.  At  4,500  to  24,000  feet.  From  clouds 
of  this  type  rain  usually  falls. 

Airship  and  Balloon  Weather 

The  most  favorable  weather  for  airships  and  bal- 
loons is  in  calm  or  Hght  winds,  when  visibility  is  good, 
extends  over  a  large  area,  over  the  whole  of  the  area 
to  be  traversed,  and  when  the  conditions  existing  are 
liable  to  persist  for  a  period  of  many  hours.  The 
characteristic  conditions  associated  with  the  cen- 
tral part  of  an  area  of  high  barometric  pressure,  or 
anti-cyclone,  are  the  most  favorable.  In  a  region  of 
this  nature  the  pressure  is,  as  a  rule,  above  the  nor- 
mal, good  weather  may  be  expected;  bad  weather 
does  not  usually  begin  imtil  the  barometer  has  been 

falling  for  several  hours. 

76 


METEOROLOGY 

Buys  Ballot's  Law 

This  law  is  a  necessary  consequence  of  the  rotation 
of  the  earth  and  may  be  enunciated  thus: 

In  the  northern  hemisphere  stand  with  your  face 
to  the  wind  and  the  barometric  pressure  will  be  lower 
on  your  right  hand  than  on  yotu"  left.  In  the  south- 
ern hemisphere  it  is  the  reverse. 

Conversion  of  Temperature 

From  Centigrade  to  Fahrenheit. 

C^  _F-32 
5  9 

How  to  ascertain  density  of  atmosphere  if  given  temperature 
and  pressure. 

P  =  Pressure  in  inches 
P  =  1.36  X  p  X  T 

P 


Therefore:  o  = 


1.36  X  T 


of  mercury 

p  =  Density  in  pounds 
per  cubic  foot 

T  =  Absolute  tempera- 
ture 


Change   in   Temperature    (Fahrenheit)    Relative  to   the 

Height 

The  decrease  in  the  temperature  relative  to  the 
height  is  one  degree  in  every  273  feet.  For  all  prac- 
tical purposes  it  may  be  considered  as  one  degree  in 
every  300  feet. 

77 


VII 

CONSTRUCTION 

Materials 

THE  choosing  of  materials  for  the  construction 
of  aircraft  has  been  and  is  at  present  a  study 
in  itself.  To  obtain  the  maximum  strength  and 
reliability  out  of  the  minimum  weight  is  our  problem. 
This  problem  has  been  solved  sufficiently  to  permit 
successful  flying,  although  there  is  still  room  for  vast 
improvement. 

First  it  is  advisable  for  the  student-pilot  to  have  a 
knowledge  of  the  materials  used  in  the  construction 
of  aeroplanes  and  the  reasons  for  their  respective 
use. 

Woods 

Ash  is  used  for  main  spars,  chassis  struts,  skids, 
flanges  of  ribs,  the  longerons  of  the  fuselage,  and  for 
engine-bearers.  It  is  a  straight-grained  wood  and 
very  tough,  but  rather  heavy.     It  is  not  obtainable 

78 


CONSTRUCTION 

in  great  lengths,  and  in  the  construction  of  fuselages 
splicing  is  often  necessary.  This  wood  has  the  ad- 
vantage of  being  easily  bent,  if  carefully  steamed, 
without  splitting. 

Spruce  is  used  for  main  spars,  also  struts  and  ribs. 
This  is  also  a  straight-grained  wood  and  is  obtainable 
in  great  lengths.  It  is  not  as  strong  as  ash,  but  con- 
siderably lighter.  In  compression  its  strength  for 
weight  is  very  great.  Silver  spruce  is  preferable  and 
always  used  when  obtainable. 

Hickory  is  frequently  used  for  landing-chassis 
struts,  especially  in  the  construction  of  heavy  ma- 
chines, on  account  of  its  capability  of  resisting  great 
shocks.  It  is  a  very  heavy  wood,  and  therefore  not 
used  in  the  construction  of  scouts  and  light  machines. 

Canadian  Elm.  This  is  a  very  tough  wood, 
though  easily  twisted  or  warped,  and  is  frequently 
used  instead  of  ash  for  engine-bearers  and  longerons. 
Its  one  great  advantage  is  that  it  will  not  snap. 

Basswood.  Used  in  the  webs  of  ribs.  It  is  a  very 
tough  wood  and  has  considerable  resiliency. 

Walnut.  Used  in  the  construction  of  propellers. 
A  hard,  close-grained  wood  and  not  apt  to  bend  or 
split. 

Mahogany.  Also  used  in  propeller  construction 
and  has  the  same  advantages  as  walnut. 

Three-ply  Wood.     What  is  known  as  three-ply 

79 


THE  EYES  OF  THE  ARMY  AND  NAVY 

wood  is  used  in  the  construction  of  fuselages  and 
nacelles  and  frequently  used  for  covering  those  parts 
of  the  planes  which  serve  as  a  footboard  when  getting 
in  and  out  of  a  machine.  It  is  also  largely  used  in 
the  construction  of  floats  for  seaplanes.  The  ma- 
terial consists  of  three  very  thin  layers  of  wood, 
placed  in  such  a  way  that  the  grains  of  the  wood  do 
not  lie  in  the  same  direction.  This  method  gives  the 
material  considerable  strength  for  weight  and  equal 
strength  in  all  directions. 

Metals 

Aluminium.  Used  for  engine-cowls,  supports  for 
wind-screens  and  control  wheels.  It  is  a  very  light 
material,  but  very  unsuitable  for  resisting  shock  or 
tension,  and  is  apt  to  crack  if  subject  to  friction. 
This  metal  suffers  extensively  under  the  influence  of 
moisture,  and  especially  where  salt  is  present.  It  is 
very  unsuitable  for  seaplanes,  and  if  used  in  their 
construction  requires  careful  watching  and  constant 
cleaning. 

Duralumin.  This  metal  is  seldom  used,  and  oc- 
casionally instead  of  aluminium.  It  is  a  very  light 
metal  and  approaches  the  tenacity  of  mild  steel.  Its 
one  great  advantage  is  that  it  can  stand  excessive 
distorting  without  loss  of  usefulness. 

§9 


CONSTRUCTION 

Manganese.  A  very  tough  metal,  and  on  account 
of  its  properties  of  resisting  corrosion  it  is  very  ad- 
vantageous in  the  construction  of  seaplanes.  Used 
for  wood-screws  and  bearing  for  rotary  parts. 

Phosphor-bronze.  Very  similar  to  manganese 
and  used  for  similar  purposes. 

Steel.  Used  for  struts,  sockets,  junction  of  spars, 
control  leads,  wire  attachments,  and  in  fact  for  al- 
most all  the  fittings  of  a  machine.  A  few  constructors 
have  made  use  of  steel  for  the  whole  framework  of  a 
machine  and  have  been  very  successful;  however, 
the  disadvantage  is  the  increased  difficulty  of  repair. 
Steel  tubes  are  now  used  for  the  interior  of  struts, 
and  in  some  cases  the  tubes  have  been  stream-lined 
with  steel  sheeting.  In  experiments  of  this  kind  one 
great  advantage  has  been  discovered.  When  a  ma- 
chine receives  a  shock  something  has  to  take  the 
shock  effect.  It  was  found  that  a  steel  tube  in  'a 
strut  or  a  steel  strut  would  bend  and  crumple  up, 
thus  absorbing  the  shock  gradually,  while  in  the 
case  of  a  wooden  strut  it  would  usually  split  or  snap 
and  the  broken  ends  cause  further  damage  to  the 
machine. 

Fabric 

Ordinary  linen  and  Egyptian  cotton  are  the  prin- 
cipal materials  used  for  covering  of  aeroplane  wings, 

8i 


THE  EYES  OF  THE  ARMY  AND  NAVY 

fuselages,  and  nacelles.  The  warp  and  weft  threads 
should  be  of  a  uniform  thickness  throughout  and  a 
good  length,  as  joints  in  the  threads  cause  weak  spots 
in  the  fabric.  Some  fabrics  have  what  is  known  as 
guide- threads.  These  are  extra-stout  threads  and 
woven  at  intervals  both  in  the  warp  and  in  the  weft, 
and  are  for  the  purpose  of  localizing  a  split  or  flaw. 

Securing  and  Repairing  Fabric.  On  no  ac- 
count should  glue  be  used  or  be  allowed  to  come  in 
contact  with  the  fabric,  as  glue,  when  hard,  has  sharp 
edges  and  may  cut  the  material.  Before  securing 
the  fabric  it  is  important  that  all  sharp  edges  of  ribs 
and  spars  be  rounded;  to  insure  that  the  fabric  is 
well  laid  on,  warp  and  weft  to  the  fore-and-aft  Une 
of  the  wing  section.  This  method  equalizes  the 
strength  in  the  warp  and  weft.  The  fabric  should  be 
either  sewn  or  tacked  on  to  the  ribs.  If  the  latter 
method  is  adopted  a  strip  of  rough  tape  should  be 
placed  along  the  line  of  tacks  in  order  to  take  the 
wear  of  the  tacks.  A  washer  should  be  placed  under 
the  head  of  each  tack.  Brass  or  copper  tacks,  with 
shanks  of  the  same  material,  should  be  used.  Steel 
tacks  are  frequently  used,  but  owing  to  their  liabiUty 
to  rust  and  therefore  destroy  the  fabric  they  should 
be  avoided. 

To  Repair  a  Tear  in  the  Fabric  when  Away 
FROM  an  Aerodrome.     On  having  a  forced  landing 

82 


CONSTRUCTION 

a  pilot  may  often  discover  a  slight  tear  in  the  fabric, 
and,  to  use  the  appropriate  term,  "A  stitch  in  time 
saves  a  thousand."  This  slight  tear,  however  sUght, 
should  be  attended  to  before  a  pilot  continues  on  his 
flight.  I  have  found  the  following  a  very  good 
method : 

Obtain  needle  and  thread  (one  can  usually  obtain 
the  required  articles  from  any  farm-house)  and  stitch 
the  edges  of  the  fabric  together  with  a  "figure-eight" 
stitch.  This  will  serve  the  purpose  of  the  pilot  until 
he  reaches  an  aerodrome,  assuming  that  the  tear  is 
not  a  large  one,  in  which  case  it  would  be  advisable 
to  wait  and  have  the  fabric  properly  attended  to. 

Repairing  a  Tear  in  the  Fabric  at  an  Aero- 
drome. This  is  somewhat  different  to  the  above  pro- 
cedure. First,  it  is  imperative  that  the  fabric  in 
the  vicinity  of  the  tear  be  thoroughly  cleaned,  then 
the  two  edges  drawn  together  with  a  figure-eight 
stitch.  A  patch  of  fabric,  overlapping  the  tear  by 
about  two  inches,  should  be  placed  over  the  rent, 
and  after  fraying  the  edges  the  patch  should  be  well 
doped.  When  the  dope  is  dry  a  larger  patch,  frayed 
at  the  edges,  should  be  placed  over  the  first  patch 
and  doped  thoroughly. 

Dope.  Dope  is  used  for  stretching  the  fabric  taut 
after  it  has  been  secured.  It  also  preserves  the  fabric 
from  deterioration  caused  by  water,  oil,  heat,  and 

83 


THE  EYES  OF  THE  ARMY  AND  NAVY 

general  weather  conditions.  Experiments  have  shown 
that  good  dope  increases  the  tensile  strength  of  fabric, 
but  makes  it  more  liable  to  tear  than  the  undoped 
material.  In  order  to  render  the  dope  fluid  enough 
to  work  into  the  fabric  it  is  necessary  to  add  spirit. 
As  the  dope  is  applied  to  the  fabric  the  spirit  evapo- 
rates. Some  spirits,  used  for  dissolving  the  dope,  are 
very  detrimental  to  the  fabric.  These  are  generally 
the  cheaper  kind;  only  the  best  should  be  used. 
Spirit  of  any  description  is  detrimental  to  metal  and 
generally  causes  rust;  therefore,  too  much  precaution 
in  protecting  the  parts  of  metal  which  come  in  con- 
tact with  the  dope  with  paint  or  grease  cannot  be 
taken.  Several  constructors  have  adopted  the  method 
of  applying  a  coat  of  varnish  over  the  dope.  This 
affords  an  excellent  protection  against  water  and  oil, 
but  is  highly  inflammable.  At  the  present  time  ex- 
periments are  being  carried  out  in  an  effort  to  obtain 
a  fluid  that  will  protect  against  moisture,  oil,  general 
weather  conditions,  and  also  be  fireproof. 

Wires 

Two  types  of  wire  are  used,  the  solid-drawn  and 
the  flexible  cable.  Control  wires,  flying-  and  landing- 
wires  are  always  of  the  latter  material.  The  solid- 
drawn  type  is  used  for  all  bracing  purposes  where  the 

84 


CONSTRUCTION 

safety  of  the  machine  in  the  air  does  not  depend  di- 
rectly on  the  wiring. 

Flexible  Cable  This  type  has  many  advantages 
over  the  soUd-drawn  type.  It  shows  chafe  at  once, 
the  outer  strands  chafing  through  first,  and  the  broken 
ends  can  be  plainly  seen.    It  also  has  a  slight  resiHency. 

Attaching  Flexible  Cable.  The  method  usually 
employed,  when  an  attachment  or  join  has  to  be  made, 
is  to  make  a  small  loop  in  the  end  of  the  wire  and 
attach  by  means  of  a  steel  fitting  or  pin.  When  making 
the  loop  the  end  of  the  pin  should  be  spliced  and  the 
spHce  either  boimd  by  a  single-strand  flexible  wire 
or  by  soldering. 

Solid-drawn  Wire.  This  wire  is  much  stronger  for 
its  diameter  than  cable  and  much  easier  to  attach.  Its 
disadvantages  are  that  it  does  not  show  wear,  is  liable 
to  snap  suddenly,  and  has  very  little  or  no  elasticity. 

Method  of  Attaching  Solid-drawn  Wire.  The 
usual  method,  and  the  most  simple  and  most  practical, 
is  by  means  of  a  steel  ferrule.  ^j^^^a    y^^stx 

The  ferrule  should  be  made  of  casssssSZZK.^J' 
metal,  solid-drawn,  and  the  ma- 
terial sHghtly  thicker  than  the  '"'s-^ 

,.  .  J.  ,1  .  rrvi.       I.     1        METHOD   OF   ATTACHMENT 

diameter  of  the   wire.     The  hole    for  solid-drawn  wire 
through  the  ferrule  should  be  of 
a  diameter  to  allow  two  wires  to  pass  through.     The 
ferrule  is  sHpped  over  the  end  of  the  wire  and  the  end 
7  8s 


THE  EYES  OF  THE  ARMY  AND  NAVY 

of  the  wire  then  placed  on  to  the  steel  attachment,  by 
the  means  of  a  small  loop,  and  the  end  of  the  wire 
then  placed  through  the  ferrule.  The  ferrule  should 
then  be  forced  as  close  as  possible  to  the  point  of 
attachment  and  the  end  of  the  wire  bent  over  the 
outside  of  the  ferrule.     (Fig.  34.) 

Strength  of  Wires  and  Flexible  Cables 

The  following  lists  have  been  obtained  from  experi- 
ments and  practical  tests  and  are  sufficient  for  all 
practical  purposes : 

Solid-drawn  Wire 

Gauge  Breaking  Load 

Number  in  Pounds 

8 2,750 

10 2,280 

12 1,720 

14A 1,170 

14B 825 

16A 520 

16B 450 

Flexible  Cable 

Circumference  Breaking  Load 

in  Inches  in  Pounds 

yi 4,500 

¥% 3,600 

-^ 1.650 

yi 1,350 

1^ 650 

86 


CONSTRUCTION 
Construction  of  Principal  Parts  of  an  Aeroplane 

For  all  practical  purposes  an  aeroplane  may  be 
divided  into  four  principal  parts:  wings,  body  (fuse- 
lage or  nacelle),  tail,  and  landing-chassis. 

Wings.  Wings  consist  of  main  spars,  ribs,  inter- 
plane  struts,  fabric,  and  wiring.  The  main  spars,  two 
in  each  plane,  the  front  and  the  rear,  are  usually 
of  wood  and  may  be  either  solid  or  built  up.  If  solid, 
they  are  generally  made  of  silver  spruce  or  ash,  and 
if  built  up  a  combination  of  spruce  and  ash  is  used. 
Frequently  constructors  are  imable  to  get  materials 
for  solid  spars  in  the  required  length,  and  it  is  neces- 
sary to  make  the  spars  out  of  two  or  more  pieces  of 
material.  This  is  done  by  means  of  a  long  glued 
scarfe  securely  bound  with  whipcord  or  glued  canvas. 
The  sections  of  solid  spars  vary  in  shape,  depending 
upon  the  bending  strain  in  the  particular  type  of  ma- 
chine for  which  the  spar  is  designed.  For  the  sake  of 
lightness  spars  are  generally  hollowed  out,  and  in 
section  they  somewhat  resemble  the  letter  I.  The 
majority  of  built-up  spars  are  also  of  this  shape  in 
section.  In  the  construction  of  built-up  spars  the 
webs  and  flanges  of  the  I  are  sometimes  of  different 
materials;  often  the  I  is  solid  and  has  a  different 
material  attached  to  the  indentation  on  each  side,  so 
as  to  form  a  square  spar. 

87 


THE  EYES  OF  THE  ARMY  AND  NAVY 

Ribs.  The  ribs  give  the  wings  their  shape  and 
they  complete  the  framework  to  which  the  fabric  is 
attached.  They  also  take  the  compression  between 
the  front  and  rear  main  spars.  In  many  types  of 
planes  there  are  both  compression  ribs  and  former 
ribs,  and  they  may  be  **made  up"  or  solid.  The  com- 
pression ribs  take  up  the  whole  of  the  compression 
between  the  spars  and  will  always  be  found  at  the 
point  of  attachment  of  struts,  of  flying-wires,  landing- 
wires,  and  drift  wires.  Former  ribs  are  lighter  in 
construction  and  are  used  for  maintaining  the  shape 
of  the  wing. 

Struts.  All  interplane  struts  of  a  biplane  are  in 
compression.  They  may  be  either  solid  or  "built  up." 
When  soHd,  spruce  is  generally  used,  and  when  built 
up,  ash  and  spruce.  Steel  struts  are  now  used  con- 
siderably and  in  most  practical  experiments  have 
given  excellent  results.  They  are  constructed  in  the 
form  of  a  tube  and  are  usually  plugged  with  spruce 
in  part  or  the  whole  of  their  length.  In  section 
they  are  either  oval,  for  stream-Hne  effect,  or  circular. 
The  lattertype  has,  so  far,  given  the  best  results,  and 
the  struts  are  always  stream-lined  by  a  shaped  wood 
backing. 

Attachment  of  Struts.  The  strut  attachments 
most  used  and  which  give  the  best  results  are  the 
metal-socket  type;    these  are  secured  to  the  main 


CONSTRUCTION 

spars  in  some  cases  by  bolts  passed  through  the  spar 
or  by  means  of  a  metal  strap,  or  a  bolt  in  the  shape 
of  a  U  passing  round  the  spar.  The  latter  method  is 
the  most  preferable. 

Wiring 

This  is  one  of  the  most  important  factors  in  the 
construction  of  aeroplanes.  For  all  practical  purposes 
wiring  can  be  divided  into  four  principal  kinds: 
flying,  landing,  drift,  and  incidence  wires.  Flying- 
wires  are  generally  of  flexible  cable  and  in  duplicate; 
each  wire  of  sufficient  strength  to  support  the  plane  or 
bay  that  it  is  designed  to  support.  Flying-wires  are 
those  which  transmit  the  loading  from  bay  to  bay,  in 
a  biplane,  and  lead  from  the  upper  attachment  of  the 
interplane  struts  to  the  bottom  attachment  of  the 
next  strut  inward,  and  in  the  inner  bay  the  wires  are 
attached  to  the  bottom  of  one  of  the  vertical  members 
of  the  fuselage.  In  the  case  of  a  pusher-type  machine, 
the  inner-bay  flying-wires  are  secured  to  the  bottom 
of  the  struts  that  are  placed  vertically  alongside  of  the 
nacelle. 

Flying-wires.  It  should  be  borne  in  mind  that 
when  a  machine  is  in  the  air  the  wings  are  supporting, 
practically,  the  whole  weight  of  the  machine  by  their 
lift.  It  will  be  readily  seen- that,  if  no  flying- wires 
were  attached,  the  hft  on  the  wings,  being  so  great, 

89 


THE  EYES  OF  THE  ARMY  AND  NAVY 

would  cause  the  wings  to  fold  up  under  the  weight  of 
the  fuselage  and  the  dead  weights  of  the  machine, 
such  as  engine,  tanks,  pilot,  and  passenger.  Several 
cases  have  been  known  where  pilots  have  met  disaster 


Fig.  35 


U — Landing-wires. 
J — ^Flying- wires. 
S — Bracing-wires. 

when  the  flying-wires,  not  being  of  a  strength  sufficient 
to  overcome  the  lift,  have  broken  and  the  wings  have 
folded  up. 

Flying-wires  are  best  known  by  pilots  by  the  expres- 
sion "down  and  in,"  on  account  of  their  leading  in 
that  direction  when  seated  in  the  machine.  Landing- 
wires  are  known  as  "down-and-out"  wires.    (Fig.  35.) 

Landing-wires.  Landing-wires,  in  a  biplane,  lead 
from  the  top  of  each  strut  to  the  bottom  of  the  next 
strut  outward.  These  wires  are  usually  single  and 
generally  made  of  flexible  cable.  The  safety  of  the 
machine,  when  in  the  air,  does  not  in  any  way  depend 
on  these  wires. 

As  the  flying-wires  support  the  weight  of  a  machine 

90 


CONSTRUCTION 

when  in  the  air,  in  a  similar  manner  the  landing-wires 
support  practically  the  whole  weight  of  the  planes 
when  on  the  ground.  If  no  landing-wires  were  at- 
tached to  an  aeroplane  the  wings  would  be  liable  to 
collapse.  Frequently,  when  a  machine  "pancakes" 
the  strain  overcomes  the  landing-wires  and  the  wings 
break  down. 

Drift  Wires.  When  a  machine  is  flying,  the  for- 
ward motion  qf  the  machine  creates  much  resistance 
of  the  air  and  this  resistance  has  a  tendency  to  sweep 
back  the  planes.  To  counteract  this  sweep-back, 
drift  wires  are  used  and  are  usually  attached  to  the 
front  of  the  engine-bearers  in  a  tractor,  and  extend  to 
the  front  outer  struts.  In  a  pusher-type  machine  they 
are  generally  attached  to  the  front  of  the  outriggers 
or  to  the  nacelle,  and  extend  to  the  outer  struts.  These 
wires  are  known  as  flying  drift  wires  and  are  frequently 
in  duplicate;  however,  many  of  the  latest  types  of 
scouts  are  not  fitted  with  these  drift  wires.  Landing 
drift  wires  are  not  so  important  as  the  flying  drift 
wires.  These  are  attached  to  the  rear  outer  strut  and 
lead  back  to  a  position  just  in  front  of  the  tail  plane 
in  a  tractor;  in  a  pusher  type  they  extend  to  the  tail 
booms.  But  in  nearly  all  of  the  latest  types  these 
landing- wires  have  been  abandoned. 

The  horizontal  cross-bracing  wires,  inclosed  in  the 
fabric  inclosure  and  considered  part  of  the  construc- 

91 


THE  EYES  OF  THE  ARMY  AND  NAVY 

tion  of  the  plane,  are  also  drift  wires,  although  they 
serve  to  prevent  the  ribs  from  flattening  out  and  losing 
their  curvature.  These  wires  are  attached  to  the  main 
spars  at  positions  where  the  flying-  and  landing-wires 
and  the  struts  meet.  They  are  also  known  as  flying 
drift  wires  and  landing  drift  wires.  The  former  lead 
to  the  rear  of  the  plane  and  out,  from  a  person  seated 
in  the  machine,  and  the  latter  to  the  front  of  the  plane 
and  out. 

Incidence  Wires.  Incidence  wires  are  used  in 
rigid  wings  to  adjust  and  maintain  the  angle  of  a  wing 
in  relation  to  the  body  of  the  machine  and  take  the 
form  of  vertical  cross-bracing  between  the  front  and 
rear  struts  of  each  bay.  These  wires  are  usually  of  the 
solid-drawn  type. 

Method  of  Adjusting  Wire.  "Tumbuckles"  are 
generally  used  when  wire  attachments  are  made. 
These  tumbuckles  allow  the  wire  to  be  slackened  or 
tightened  and  should  have  sufficient  threads  engaged 
to  insure  their  safety,  and  should  be  properly  locked 
to  avoid  any  possibihty  of  their  unscrewing  through 
vibration. 

The  Body 

The  body  of  a  tractor-type  machine  is  termed  the 
fuselage,  and  in  the  pusher  type  the  body  is  termed  the 
nacelle.     The  body  of  an  aeroplane  generally  carries 

92 


CONSTRUCTION 

the  dead  weights,  consisting  of  engine,  tanks,  pilot, 
passenger,  and  freight ;  it  also  carries  the  forward  mo- 
tion from  an  engine  to  the  machine ;  therefore  it  should 
be  rigidly  attached  to  the  planes.  In  biplanes  of  the 
former  type  the  main  spars  of  the  lower  planes  are 
usually  passed  through  the  sides  of  the  body  and  con- 
nected together  by  means  of  a  steel  box  fitting,  half- 
way between  the  two  sides  and  in  the  center  line  of  the 
fuselage. 

In  types  of  machines  such  as  the  Caudron,  which 
has  a  short  body,  the  lower  planes  are  usually  con- 
tinuous right  across,  forming  one  plane  throughout; 
it  is  attached  to  the  main  spars  by  means  of  bolts  and 
to  the  upper  plane  by  means  of  struts  and  bracing- 
wires. 

The  main  foundation  and  engine-bearers  of  all  bodies 
are  strong  longitudinals,  usually  of  ash.  These  longi- 
tudinal members  are  connected  by  vertical  and  hori- 
zontal members  of  spruce  and  ash,  and  are  cross- 
braced  with  wires  between  each,  both  horizontally  and 
vertically.  The  vertical  members  on  each  side  are 
also  cross-braced  diagonally  across  the  body.  These 
longitudinals  are  usually  made  up  of  two  or  more 
lengths  of  material.  The  splices  are  always  aft  of  the 
pilot's  seat  and  are  enforced  by  long  steel  box  fittings. 
Immediately  behind  and  to  the  front  of  the  pilot's 
seat  the  longitudinals  are,  as  a  rule,  much  thicker  than 

93 


THE  EYES  OF  THE  ARMY  AND  NAVY 

the  portions  that  extend  to  the  tail  of  the  machine. 
The  vertical  and  horizontal  members  are  also  stouter 
and  placed  closer  together  in  the  fore  part  of  the  fuse- 
lage than  in  the  rear  portion.  In  several  types  of 
aeroplanes  a  portion  of  the  longitudinals  serve  as 
engine-bearers  and  are  protected  from  deterioration, 
due  to  oil,  by  a  steel  casing. 

Fuselage  and  Nacelle  Covering 

Fabric  is  the  chief  material  used  for  covering  fuse- 
lages and  nacelles,  but  aluminium  and  three-ply 
wood  are  sometimes  used.  The  latter  is  always  used  in 
types  where  perfect  stream-line  effect  is  desired.  The 
use  of  this  material  adds  greatly  to  the  strength  of  the 
machine.  In  short  bodies  the  floor,  and  frequently 
the  end  of  the  body,  which  is  either  pointed  or  rounded 
off,  is  constructed  of  three-ply. 

The  Tail 

The  construction  of  the  tail  plane  is  very  similar  to 
the  construction  of  the  main  planes.  There  are  two 
distinct  types  of  tails,  the  non-lifting  and  the  lifting 
tail,  the  only  difference  being  that  the  latter  is  de- 
signed to  carry  a  portion  of  the  weight  of  the  machine. 
A  lifting  tail  has  a  tail  plane  with  cambered  upper 

94 


CONSTRUCTION 

surface,  similar  to  an  ordinary  plane,  and  a  non-lifting 
tail  has  a  tail  plane  that  is  fiat;  this  may  be  defined 
as  a  horizontal  fin  to  give  steadiness  in  a  fore-and-aft 
direction.  There  are  also  non-lifting  tails  which  have 
both  upper  and  lower  surfaces  of  the  tail  plane  cam- 
bered. Some  types  of  machines  have  the  leading  edge 
of  the  tail  plane  curved;  in  these  types  a  steel  tube 
usually  forms  the  leading  edge  and  main  spar  com- 
bined. The  trailing  edge  of  tail  planes  is  usually  con- 
structed of  metal  and  thus  forms  the  rear  spar.  To 
this  trailing  edge  is  attached  the  elevator  plane  in 
the  case  of  a  "hinge "  tail.  There  are  various  methods 
of  attaching  this  flap  to  the  tail  plane.  Pintals  and 
gudgeons,  similar  to  the  method  employed  to  attach 
a  rudder  to  a  ship,  are  used  frequently;  but  when  a 
steel  tube  forms  the  rear  spar  and  trailing  edge,  the 
method  of  steel  straps  passing  round  the  tube  and  free 
to  revolve  round  it  is  advised ;  this  is  the  method  usu- 
ally adopted. 

In  the  case  of  the  "warp"  tail  the  rear  portion  and 
trailing  edge  of  the  tail  plane,  being  flexible  and 
capable  of  being  moved  up  and  down,  performs  the 
elevator  functions  of  the  machine.  Aeroplanes  with 
inclosed  fuselages  usually  have  the  tail  plane  at- 
tached to  the  longitudinals  by  means  of  U-bolts.  In 
machines  of  this  type  the  rudder  post  is  rigidly  con- 
nected  to   the   ends   of   the  longitudinal   members. 

95 


THE  EYES  OF  THE  ARMY  AND  NAVY 

Machines  with  nacelles  such  as  a  Farman,  or  very 
short  open  bodies,  as  a  Caudron,  are  equipped  with 
open  or  box  tails.  In  such  machines  the  tail  plane, 
elevator,  and  rudder  are  attached  to  the  outriggers; 
these  consist  of  four  horizontal  members,  connected 
together  by  struts  and  cross-bracing.  These  out- 
riggers are  attached  to  the  rear  spars  of  the  upper 
and  lower  planes  on  either  side  of  the  body.  Wires 
extending  from  the  rear  outer  interplane  struts  to 
the  rear  ends  of  the  outriggers  hold  the  outriggers 
in  their  respective  positions.  A  tail  cell  is  attached 
to  the  end  of  these  outriggers  and  usually  consists 
of  upper  and  lower  tail  plane,  upper  and  lower  ele- 
vator plane,  and  one,  two,  or  more  rudders.  This  tail 
cell  is  connected  together  by  means  of  small  struts 
and  wire  bracing. 

The  Landing-chassis  or  Undercarriage 

The  landing-chassis,  usually  termed  the  under- 
carriage, has  two  forces  to  resist:  the  vertical  shock 
of  landing  and  the  horizontal  force  tending  to  sweep 
the  undercarriage  backward  when  the  machine  is 
running  along  the  ground.  These  forces  vary  greatly. 
The  former  is  great  when  a  machine  is  "pancaked," 
and  the  second  strain  is  greatest  in  a  fast  landing  on 
rough   or  soft   ground.     These  two  forces  are  best 

96 


CONSTRUCTION 

resisted  by  placing  the  principal  landing-chassis 
struts  in  the  direction  of  the  resultant  force  of  the 
two  strains.  For  instance:  if  the  principal  struts 
are  placed  sloping  forward,  from  the  fuselage  to  the 
skid,  or  axle,  of  the  machine,  the  vertical  force  of 
landing  will  have  a  tendency  to  thrust  the  under- 
carriage forward,  and  by  doing  so  will  counteract  the 
horizontal  force  which  is  created  when  the  wheels 
are  checked  by  the  ground.  In  the  majority  of 
fast  scouts,  where  weight  and  resistance  are  important 
factors,  the  undercarriage  is  comparatively  narrow 
and  usually  consists  of  two  struts  on  each  side  joined 
together  at  the  bottom  in  the  form  of  a  V.  These 
struts  are  very  stout  and  may  be  made  of  steel, 
ash,  or  spruce.  The  V  is  attached  to  a  continuous 
axle  by  means  of  rubber  shock-absorbers.  In  the 
slower  and  heavier  type  of  machines  ash  skids  are 
usually  fitted  and  are  connected  to  the  struts  by  steel 
fittings. 

All  undercarriages  are  cross-braced,  generally  by 
means  of  strong  flexible  cable,  and  in  types  where 
long  skids  are  used  transverse  struts  or  transverse 
wires  are  used. 

In  machines  that  have  short  bodies,  such  as  the 
Caudron  type,  the  two  sides  of  the  undercarriage 
are  attached  to  the  lower  planes  under  the  interplane 
struts.    In  such  machines  the  undercarriage  is  much 

97 


THE  EYES  OF  THE  ARMY  AND  NAVY 

wider  and  is  equipped  with  a  short  axle  and  a  wheel 
at  each  end  on  each  side  of  the  landing-chassis. 

Undercarriages  are  usually  placed  so  that  the 
wheels  are  at  the  point  of  center  of  gravity;  but 
in  many  types  of  machines  this  rule  has  been  some- 
what disregarded  in  order  to  allow  for  peculiarities 
in  the  design.  However,  if  the  wheels  are  placed  too 
far  behind  the  center  of  gravity  the  machine  will 
have  a  tendency  to  pitch  forward  on  landing,  and  if 
the  wheels  are  placed  too  far  in  front  the  machine 
on  landing  will  be  inclined  to  bounce  and  slew  round 
quickly  on  the  ground  if  traveling  fast  or  the  direction 
of  motion  is  altered.  This  will  be  observed  when 
landing  or  taxi-ing  a  machine  of  the  Nieuport  type; 
however,  the  tendency  to  bounce  can  be  avoided  if 
the  following  method  is  adopted.  When  the  machine 
touches  the  ground,  instead  of  pulling  back  the  "joy- 
stick" or  control  lever,  as  in  the  case  when  landing 
the  majority  of  machines,  push  the  control  lever  for- 
ward slightly.  This  movement  will  keep  the  tail  off 
the  ground  until  the  forward  speed  of  the  machine 
has  slackened  somewhat  and  the  tail  drops  of  its  own 
accord. 

The  Controls  of  a  Machine 

The  standard  method  of  control  adopted  is  rudder 
control  by  means  of  a  foot-bar  or  pedals,  and  a  control 

98 


CONSTRUCTION 

lever,  commonly  termed  a  "joy-stick"  or,  in  the  case 
of  a  Curtiss  machine,  a  control  wheel.  The  elevator  is 
controlled  by  the  fore-and-aft  movement  of  the 
lever  or  wheel,  and  the  lateral  or  aileron  control  by  a 
lateral  movement  of  the  "joy-stick"  or  rotation  of  the 
wheel.  Rotation  or  movement  of  the  control  lever 
in  a  direction  to  the  plane  on  which  less  lift  is  desired. 

Control  Wires.  All  control  wires  should  be  of  the 
flexible-cable  type  and  should  be  in  duplicate;  as  also 
their  attachments.  When  control  wires  lead  round 
angles  some  type  of  belt  or  semicircular  crank  is  ad- 
visable. Sheaves  and  copper  fairleads  are  usually 
used.  The  elevator  and  rudder  control  wires  are 
usually  attached  to  a  V  piece  or  a  king  post.  In  the 
construction  of  rudders  this  king  post  should  be  bolted 
on  to  the  rudder  post.  In  some  types  it  is  bolted  on 
to  the  central  rib,  but  the  former  method  is  preferable. 
A  light  steel  tube,  bent  into  the  required  shape,  cross- 
connected  by  horizontal  wood  ribs  and  covered  with 
fabric,  usually  forms  the  rudder.  The  rudder  post 
passes  through  these  wood  ribs  and  is  secured  to  the 
steel  tube  at  the  top  and  bottom,  usually  by  welding. 

The  elevator  control  and  construction  is  similar  to 
the  rudder.  In  many  types  of  machines,  owing  to 
the  length  of  the  elevator  flap,  it  is  necessary  to  fit 
two  king  posts,  one  toward  either  end,  and  this 
necessitates  a  double  set  of  control  wires.     A  light 

99 


THE  EYES  OF  THE  ARMY  AND  NAVY 

steel  tube  usually  forms  the  main  spar  to  which  ribs 
are  fitted.  They  should  be  rigidly  attached  by  means 
of  metal  flanges.  Some  types  have  the  steel  tube  bent 
to  form  the  outline  of  the  elevator.  Frequently  wood 
is  used  for  the  sides  and  a  light  wood  or  metal  strip 
to  maintain  the  shape  of  the  leading  edge.  Quite 
often  the  elevator  is  divided  into  two  portions,  the 
rudder  passing  between  them. 

Lateral  Control.  There  are  two  methods  of 
lateral  control  in  general  use,  the  warp  control  and 
the  aileron  control;  the  latter  may  be  either  double- 
or  single-acting.  In  m.achines  fitted  with  the  former 
(the  warp)  the  control  wires  pass  from  the  control 
lever  or  wheel  through  fairleads,  low  down  in  the 
body,  to  the  rear  outer  struts  of  the  warping  bay. 
There  are  various  methods  of  attaching  these  warping 
wires.  One  method  is  to  pass  the  wires  through  fair- 
leads  fitted  at  the  bottom  of  the  rear  outer  struts 
to  different  points  along  the  warping  section  of  the 
top  plane.  Only  the  top  plane  is  warped,  and  may  be 
warped  along  the  entire  length  of  the  plane  or  only 
the  outer  bay.  Warp-controlled  machines  are  fitted 
with  a  compensating  wire  which  is  usually  placed  along 
the  top  of  the  upper  plane  leading  from  one  warp 
section  to  the  warp  section  on  the  opposite  plane. 
By  this  means,  when  one  warp  section  is  pulled 
down,  by  movement  of  the  control  lever  or  wheel, 

lOO 


CONSTRUCTION 

the  opposite  warp  section  is  pulled  up  by  the  com- 
pensating wire. 

Ailerons  are  hinged  flaps  attached  to  the  rear 
extremities  of  the  planes.  They  are  always  fitted  to 
the  upper  planes  of  aileron-controUed  machines  and 
frequently  attached  to  the  lower  planes  also.  There 
are  two  methods  of  operation  of  single-acting  ailerons : 
by  wires  leading  from  the  under  side  of  the  aileron 
through  a  fairlead  on  the  rear  spar  of  the  lower  plane, 
or  by  means  of  a  vertical  king  post  on  the  under  side 
and  leading  across  the  plane  to  the  leading  edge  and 
thence  to  the  control  lever. 

The  operation  of  double-acting  aileron  control  is 
very  similar  to  single-acting;  but  from  a  king  post  on 
the  upper  side  of  the  aileron  a  compensating  wire  is 
fitted.  This  wire  is  led  across  the  upper  surface  of 
the  top  plane  to  a  fairlead  on  the  front  spar,  along 
the  front  spar  and  through  another  fairlead  and 
across  the  plane  to  a  similar  king  post  on  the  opposite 
aileron.  The  difference  in  action  of  single-  and  double- 
acting  ailerons  is:  in  the  latter  the  compensating 
wire  performs  the  same  function  as  the  warp-control 
machines,  as  described  above,  and  in  single-acting 
aileron  control  each  aileron  is  independent. 

Both  single-  and  double-acting  controls  have  their 
advantages  and  disadvantages.  In  nearly  all  of  the 
latest   types   the   double-acting   ailerons   are   fitted. 

S  lOI 


THE  EYES  OF  THE  ARMY  AND  NAVY 

The  warp  control  is  not  used  except  on  old-type  ma- 
chines mantifactured  for  school  work. 


Truing  Up  an  Aeroplane 

A  machine  is  said  to  be  "trued  up"  when  all  con- 
trols and  control  wires  have  been  thoroughly  in- 
spected and  put  in  perfect  order  and  when  the  angle 
of  incidence  and  the  dihedral  angle  have  been  ad- 
justed to  the  correct  angles  and  the  aeroplane,  in 
general,  thoroughly  inspected.  No  set  rule  or  method 
of  "truing  up"  can  be  laid  down,  as  different  con- 
structions and  different  riggers  have  slightly  different 
methods;  but  in  the  majority  of  machines  the  pro- 
cedure is  the  same.  First  it  is  necessary  to  place 
the  machine  in  a  flying  position — that  is,  in  a  po- 
sition similar  to  when  the  machine  is  flying  level.  This 
is  done  by  placing  a  stand  under  the  tail  and  stands 
under  the  wings  to  take  the  weight  of  the  body  and 
wings  off  the  undercarriage.  It  is  usual  to  place  a 
stand  each  side  of  the  fuselage  and  one  at  each  wing 
tip.  Care  should  be  taken  that  these  stands  are 
placed  under  the  interplane  struts.  The  fuselage 
should  then  be  leveled.  This  can  be  done  by  placing 
a  spirit-level  on  the  engine-bearers  and  adjusting  the 
tail  stand  until  the  body  is  level  both  fore  and  aft 
and  laterally.    The  fuselage  should  then  be  corrected 

I02 


CONSTRUCTION 

in  the  fore-and-aft  position.  A  very  common  method 
is  to  mark  a  position  half-way  down  one  of  the  vertical 
members  of  the  fuselage,  close  to  the  pilot's  seat,  and 
also  on  the  rear  vertical  member  of  the  fuselage. 
Stretch  a  string  between  the  two  points  and  this 
line  should  cut  all  the  vertical  members  at  a  point 
half-way  between  the  top  and  bottom  of  the  fuselage. 
Next  trammel  the  bags  of  the  fuselage  both  vertically 
and  horizontally.  The  undercarriage  should  then  be 
corrected  and  the  stands  supporting  the  weight  of 
the  machine  removed.  If  the  machine  is  a  type  with 
a  center  section  it  should  be  trued  up  and  adjustments 
made  if  necessary.  Landing- wires  should  then  be 
trammeled;  flying- wires  trammeled;  incidence  wires 
trammeled.  Flying- wires  should  be  slightly  slacker 
than  the  landing-wires.  While  trammeling  these 
wires  the  dihedral  angle  should  be  considered  and 
adjustments  made  if  necessary.  The  angle  of  inci- 
dence should  then  be  tested,  and  lastly  the  control 
wires  and  drift  wires,  and  adjusted  if  necessary. 


VIII 

THE  CARE  AND  MAINTENANCE  OF  AEROPLANES 

Importance 

As  an  Arab's  first  and  last  thoughts  are  for  his  f  aith- 
/A  ful  steed,  so  should  a  pilot  care  for  his  machine. 
Air-worthiness,  reliability,  and  endurance  of  a  ma- 
chine depend  largely  upon  the  care  spent  upon  it. 
Machines  should  not  be  exposed  to  extremes  of 
weather.  Wood,  no  matter  how  well  seasoned,  if  not 
protected  by  a  coat  of  varnish,  will  absorb  moisture, 
and  wiU  deteriorate  quickly.  Aeroplane  sheds  and 
hangars  should  be  kept  dry  and,  as  far  as  possible, 
at  an  even  temperature. 

When  a  machine  returns  from  a  flight  it  should  be 
thoroughly  cleaned,  as  soon  as  possible;  rust,  sand, 
mud,  and  oil,  if  left  to  dry,  will  cause  considerable 
deterioration  and  an  increased  amount  of  labor  in 
removing.  The  machine  should  be  thoroughly  ex- 
amined and  the  least  sign  of  wear  and  tear  be  at- 
tended to  promptly.  Special  attention  should  be  paid 
to  control,  aileron,  flying-  and  landing-wires  and  the 

104 


THE    CARE    OF   AN   AEROPLANE 

points  where  they  pass  round  pulleys  or  through  fair- 
leads.  Quite  often  a  pilot,  when  running  over  the 
control  wires  with  his  thumb  and  forefinger,  will  dis- 
cover a  single  strand  gone;  this  should  be  attended 
to  before  the  machine  is  flown  again.  Periodically 
a  machine  should  be  thoroughly  examined  and 
every  part  of  the  aeroplane  inspected.  Aeroplane 
engines  should  always  be  tested  and  should  run  to 
the  satisfaction  of  the  pilot  before  a  flight  is  under- 
taken. 

The  Handling  and  Transport  of  an  Aeroplane 

The  following  rules  should  be  observed  when  mov- 
ing a  machine  in  or  out  of  a  shed  or,  in  fact,  every 
time  the  machine  is  moved. 

Always  place  the  propeller  in  a  horizontal  position 
before  moving  a  machine.  Quite  often  the  tail  of  a 
machine  is  lifted  too  high  and  if  the  propeller  is  not 
thus  protected  it  is  liable  to  be  damaged  by  touch- 
ing the  ground.  The  tail  of  a  machine  should  be 
lifted  and  care  should  be  taken  that  sufficient  men 
are  told  off  for  this  work  so  as  to  avoid  risk  of  the  tail 
being  dropped  through  a  man  slipping  or  dropping 
through  fatigue.  In  the  case  of  a  tractor-type  ma- 
chine the  tail  should  be  lifted  on  the  bottom  longerons 
of  the  fuselage  at  the  base  of  the  bay  struts.    In  most 

105 


THE  EYES  OF  THE  ARMY  AND  NAVY 

machines  of  the  latest  types  an  arrow,  painted  on  the 
outside  of  the  fuselage,  indicates  the  point  at  which 
to  lift.  However,  if  there  are  no  indications  of  the 
vertical  members  of  the  body  they  can  be  easily  found 
by  passing  the  hand  along  the  side  of  the  fuselage. 
In  the  pusher  type  of  machine  the  lift  should  be 
exerted  on  the  lower  tail-booms,  close  to  and  on  either 
side  of  the  inter-tail  boom  struts.  Always  tell  off  a 
hand  to  watch  each  wing-tip  and  to  give  warning  of 
any  obstruction  to  the  person  in  charge. 

The  wheels  and  tires  of  a  machine  are  designed 
to  go  forward,  and  a  machine  should  not  be  turned 
without  moving  it  backward  and  forward;  however,  a 
machine  should  only  be  moved  backward  when  ab- 
solutely necessary.  At  all  times  pay  great  atten- 
tion to  the  wheels. 

When  pushing  or  pulling  an  aeroplane  the  force 
should  always  be  exerted  at  the  base  of  the  strut, 
and  never  on  any  occasion  should  men  be  allowed  to 
grasp  the  middle  of  the  strut.  If  when  getting  into 
and  out  of  a  machine  it  is  necessary  for  a  pilot  to 
hold  on  to  a  strut  he  should  always  endeavor  to 
grasp  it  as  near  the  upper  end  as  possible. 

The  trailing  edge  of  a  plane  is  one  of  the  weakest 
points  and  also  one  of  the  most  important;  therefore 
it  should  never  be  touched,  except  when  necessary, 
and   should   be   well   protected   at   all   times.      The 

1 06 


THE    CARE    OF   AN   AEROPLANE 

leading  edge  is  another  important  part  of  a  machine 
and  should  be  carefully  watched.  Never  lift  on  the 
tail  plane,  elevators,  rudder,  or  any  wires.  If,  on 
any  occasion,  it  is  necessary  to  move  the  elevator  and 
rudder,  when  stowing  a  machine  away,  always  move 
them  by  their  proper  controls. 

Filling  Up  Machines 

"Fill  the  oil  tank  first."  Many  machines  have  a 
petrol  gauge  and  no  oil  gauge,  and  if  the  above 
method  is  adopted  it  is  less  likely  that  the  oil  will  be 
forgotten.  Petrol  should  always  be  strained  through 
a  chamois  skin.  This  will  check  all  particles  of 
sand  and  dirt  and  will  absorb  any  water  that  may  be 
in  the  petrol.  Tank  caps  should  always  be  screwed 
down  securely.  Too  much  importance  cannot  be 
paid  to  this  matter,  especially  when  machines  are 
equipped  with  pressure  tanks.  It  is  never  advisable  to 
alter  the  position  of  any  petrol  or  oil  cock  or  tap  in  a 
machine  unless  ordered  to  do  so.  Care  should  be 
taken  that  the  outside  of  petrol  and  oil  cans  be 
kept  clean.  They  should  not  be  left  standing  on 
the  ground,  as  sand  and  dirt  thus  gathered  may 
find  their  way  into  the  tanks  and  cause  considerable 
trouble. 

Petrol  and  oil  tins  should  not  be  damaged,  as  these 

107 


THE  EYES  OF  THE  ARMY  AND  NAVY 

cans  are  usually  on  charge  and  have  to  be  returned 
for  refilling. 


Priming  or' "Doping"  an  Engine 

To  enable  an  engine  to  start  easily  it  is  primed. 
A  small  amount  of  petrol  is  forced  into  each  cylinder 
by  means  of  a  small  squirt  gun.  Care  should  be 
taken  to  avoid  spilling  petrol  over  the  exterior  of 
the  engine  and  not  to  "over-dope,"  as  both  faults 
are  liable  to  cause  trouble.  While  priming  it  is  ad- 
visable to  rotate  the  propeller  in  order  to  circulate  the 
petrol  in  the  cylinders. 

Preparations  for  Swinging  the  Propeller 

"Chocks"  should  be  placed  imder  the  wheels  be- 
fore an  engine  is  tested.  These  chocks  are  generally 
provided  with  a  long  lanyard  to  enable  them  to  be 
pulled  away  readily  by  men  stationed  at  the  wing- 
tips.  When  testing  engines  in  tractor  machines  the 
men  (except  those  required  for  holding  the  lanyards 
of  the  chocks  and  a  hand  for  the  swinging  of  the 
propeller)  should  be  in  rear  of  the  machine.  Two 
men  should  be  told  off  to  hold  down  the  tail,  at  a  po- 
sition just  in  front  of  the  tail  plane,  as  under  the  action 
of  the  slip  stream  from  the  propeller  the  tail  ha^  a  great 

io8 


THE    CARE    OF   AN   AEROPLANE 

tendency  to  lift.  Men  told  off  to  hold  struts  should 
grasp  and  pull  on  the  rear  interplane  struts  at  the 
bottom. 

In  engine  testing  on  the  pusher-type  machine  the 
strut  hands  should  push  on  the  bottom  of  the  front 
interplane  struts.  Two  hands  should  be  stationed  to 
hold  down  the  tail.  This  is  best  accomplished  by 
holding  down  on  the  inter-tail  boom  struts.  Men 
should  never  be  allowed  to  put  their  weight  on  the 
tail  booms. 

Swinging  a  Propeller 

First  make  sure  that  the  ignition  switch  is  at 
"off."  This  not  only  applies  when  actually  swinging  a 
propeller,  but  also  when  cleaning  machines  in  their 
sheds.  In  short,  never  touch  a  propeller  until  you 
have  satisfied  yourself  that  the  switch  is  off. 

In  tractors  most  rotary  engines  are  fitted  with  two- 
bladed  propellers  and  rotate  in  an  anti-clockwise 
direction,  i.e.,  when  facing  the  engine.  The  ma- 
jority of  stationary  engines  are  fitted  with  two-  or 
four-bladed  propellers  which  revolve  in  a  clockwise 
direction.  In  order  to  become  a  good  "prop"  hand 
a  great  deal  of  practice  is  required.  There  is  a  knack 
in  this  work  which  can  only  come  by  actual  swinging. 
Strength  is  an  important  factor,  but  not  nearly  so 
important  as  a  knowledge  of  using  the  weight  of  the 

109 


THE  EYES  OF  THE  ARMY  AND  NAVY 

body  properly  and  efficiently.  Although  there  are 
many  methods  of  swinging  a  propeller,  the  main 
principle,  in  all  of  them,  is  the  same.  The  following 
method  has  been  found  to  be  a  very  good  one  and 
applies  to  a  130  H.  P.  Clerget  engine  in  a  Sopwith 
scout,  although  it  can  be  applied  to  all  rotary  engines, 
whatever  the  direction  of  their  rotation  may  be,  the 
only  difference  being  a  change  in  the  position  of  the 
feet. 

Place  the  propeller  in  a  horizontal  position  just 
past  compression  in  one  of  the  cylinders.  Grasp 
the  blade  with  both  hands  as  close  together  as  pos- 
sible and  a  little  to  the  center  of  the  propeller,  half- 
way between  the  boss  and  the  tip  of  the  blade.  Arms 
and  wrists  should  be  slightly  bent.  The  left  foot 
carries  all  the  weight  of  the  body  and  should  be 
placed  about  a  foot  in  rear  of  the  hands.  The  right 
foot  should  be  clear  of  the  ground.  The  weight  of 
the  body  should  be  suddenly  transferred  to  the  pro- 
peller, the  left  foot  giving  the  body  a  swing  to  the 
right  across  the  plane  of  the  propeller.  The  grasp  of 
the  blade  should  not  be  released  until  the  blade 
passes  the  horizontal  on  the  opposite  side.  The  right 
foot  comes  down  to  the  right  of  the  boss  and  takes  up 
the  whole  weight  of  the  body.  A  part  of  a  circle  is 
described  by  the  left  foot  and  comes  down  about  a 
pace  in  rear  of  the  right  foot.     (Fig.  36.) 

no 


THE    CARE    OF    AN    AEROPLANE 

The  first  position  of  the  feet  is  shown  by  L.i.  and 
R.I.  R. I .  is  off  the  ground.  L. 2.  and  R. 2.  shows  the 
position  of  the  feet  at  the  completion  of  the  swing. 
The  Hnes  joining  L.i.  and  L.2.,  R.i.  and  R.2.  show  the 
approximate  paths  of  the  feet. 

The    four-bladed    propellers,    fitted    on    machines 


Hands  \     (^    1 


L,^, 


Fig.  36 


j     Engine 


1 I 

,.,  Boss     j-v 


Propeller 


—--CD 
L2 


such  as  the  80  H.  P,  Renault  engine  B.  E.,  require 
different  handling  on  account  of  the  blades  being 
very  thin.  Propellers  on  machines  -of  this  type 
generally  rotate  in  a  clockwise  direction  when  facing 
the  propeller.  The  "one-handed"  swing  is  recom- 
mended for  these  machines,  and  the  following  is 
usually  the  method  employed: 

Place  one  of  the  blades  at,  approximately,  the  "two 
o'clock"  position  and  with  the  right  hand  grasp  the 
blade  as  near  as  possible  to  the  boss;  swing  the  pro- 
peller by  running  across  the  front  of  the  machine. 

HI 


THE    EYES    OF   THE   ARMY   AND    NAVY 
Cleaning  the  Machines 

As  soon  as  possible  after  a  flight  a  machine  should 
be  cleaned.  All  mud,  dirt,  sand,  and  oil  should  be 
removed.  Attention  should  also  be  paid  to  the  in- 
side of  the  fuselage  or  nacelle  and  it  should  receive  a 
thorough  cleaning  periodically.  When  doing  this 
care  should  be  taken  that  no  instruments,  switches, 
or  taps  are  meddled  with.  Plenty  of  soap  and  warm 
water  is  the  best  for  aU  cleaning  purposes.  Petrol 
damages  varnish  and  paint  and  is  susceptible  to 
fire,  therefore  it  should  be  avoided.  It  will  be 
observed  that  when  the  fabric  is  washed  with  soap 
and  water  it  is  inclined  to  slacken  somewhat,  but  will 
regain  its  tautness  when  thoroughly  dry. 

If  a  machine  gets  wet  the  water  should  be  dried  off 
the  planes  as  soon  as  possible,  by  means  of  clean 
waste,  and  the  wires  should  be  greased. 

iStorage  of  Aeroplanes 

Immediately  a  machine  is  housed  a  tray  should  be 
placed  under  the  engine.  This  will  prevent  oil  from 
dropping  on  the  floors  and  therefore  save  tires  and 
greatly  assist  in  maintaining  the  general  cleanliness 
of  the  sheds.  The  weight  of  the  machine  should  be 
relieved  from  the  wheels  or  floats  by  placing  supports 

112 


THE    CARE    OF   AN   AEROPLANE 

under  the  axle.  Care  should  be  taken  that  the 
supports  are  placed  in  such  a  position  that  the 
main  weight  of  the  machine  is  evenly  distributed. 
It  is  advisable  to  take  the  weight  off  the  tail  skid  or 
tail  float,  as,  if  much  weight  is  carried,  the  main 
longerons  or  the  tail  booms  are  liable  to  be  thrown 
out  of  true  shape  by  the  constant  bending. 

Care  of  Materials 

Fabric.  It  has  been  stated  that  the  fabric  is  pro- 
tected from  damp,  oil,  and  the  general  weather  con- 
ditions by  the  application  of  dope;  however,  the 
fabric  should  be  cleaned  as  soon  as  possible  after  a 
flight;  if  moisture,  oil,  or  mud  is  allowed  to  remain 
on  the  fabric  it  will  greatly  deteriorate  the  material. 
Frequently  it  is  found  that  portions  of  the  fabric 
become  saturated  with  oil.  These  portions  should  be 
cleaned  and  redoped  thoroughly. 

Wood.  All  wood  should  be  protected  with  a  coat 
of  varnish. 

Propellers.  Propellers  should  always  be  stored  in  a 
dry  place  and  kept  as  dry  as  possible.  Exposure  to 
damp  renders  them  liable  to  warp.  They  should  be 
examined  frequently  in  order  to  see  that  the  lamina- 
tions are  not  beginning  to  separate. 

Bracing  Wires.    The  external  bracing  wires  should 

113 


THE  EYES  OF  THE  ARMY  AND  NAVY 

be  protected  by  grease  or  a  coat  of  paint.  It  should 
be  remembered  that  wires  and  fittings  when  painted 
deteriorate  quicker  than  wires  and  fittings  protected 
with  grease.  Also,  on  account  of  the  paint,  it  is  less 
easy  to  detect  deterioration.  All  internal  bracing 
wires  should  be  painted,  but  before  a  coat  of  paint  is 
applied  it  is  imperative  that  the  wires  be  perfectly 
dry  and  free  from  rust  and  grease. 

Tumbuckles,  bolts,  nuts,  and  wire-strainers  should 
be  protected  from  rust  by  a  light  film  of  oil  or  grease. 
The  turnbuckles  should  have  sufficient  threads  en- 
gaged to  insure  their  safety  and  should  be  locked  to 
prevent  any  possibility  of  their  unscrewing.  Bolts  and 
nuts  should  be  properly  tightened  and  locked  by 
means  of  split  pins  or  locknuts. 

Tires.  Grease  and  oil  are  very  detrimental  to  tires, 
therefore  they  should  be  kept  free  from  such  sub- 
stances and  should  be  kept  pumped  up. 

Field  Repairs.  If  a  pilot  has  a  forced  landing  and 
his  machine  is  only  sHghtly  damaged  he  should 
first  ascertain  the  new  parts  required  to  continue 
his  journey  and  communicate  with  his  respective 
aerodrome  for  the  parts  required.  But  it  should  be 
borne  in  mind  that  an  absolutely  correct  report  of 
parts  necessary  will  save  considerable  time  and 
trouble.  For  instance,  if  a  leading  edge  of  a  plane  is 
only  slightly  damaged  a  pilot  could  manage  to  fly 

114 


THE    CARE   OF   AN   AEROPLANE 

back  to  his  aerodrome  without  having  a  new  plane 
attached;  whereas,  if  a  tail  plane  or  rudder  has 
suffered  only  slightly,  it  would  be  necessary  to  have 
new  parts  fitted  before  attempting  to  continue  the 
journey.  If  a  machine  is  damaged  to  such  an  ex- 
tent that  the  trip  has  to  be  abandoned,  the  following 
points  in  dismantHng  and  transporting  a  machine 
should  be  observed: 

The  wings  should  be  taken  down  and  taken  apart. 
They  should  be  placed  on  their  leading  edge  after 
having  it  protected;  if  the  planes  are  placed  in 
pairs,  all  four  planes  (in  the  case  of  a  biplane)  can 
easily  be  placed  on  one  large  lorry  or  trailer.  If  the 
machine  is  a  small  type,  the  fuselage  or  nacelle  C&n 
also  be  placed  on  the  lorry  between  the  two  sets  of 
planes ;  however,  if  the  undercarriage  is  undamaged  a 
good  method  is  to  trail  the  fuselage  or  nacelle  and 
center  section. 


IX 

AERO    ENGINES 

THE  main  requirements  of  aeroplane  engines  are: 
reliability,  small  weight  per  horse  power,  small 
oil  and  petrol  consumption  per  horse  power,  a  mini- 
mum head  resistance,  and  absence  of  vibration.  There 
are  two  distinct  types  of  aero  engines,  the  rotary  and 
the  stationary.  The  former  is  always  air  cooled;  the 
latter  may  be  either  air  or  water  cooled. 

Types  of  Rotary  Engines 
Gnome,  Clerget,  Verdet,  Le  Rhone,  and  Isaacson. 

Types  of  Stationary  Air-cooled  Engines 
Renault,  Anzani,  and  De  Dion. 

Types  of  Stationary  Water-cooled  Engines 

Curtiss,  Green,  Austro-Daimler,  Chenu,  Argyll, 
Sunbeam,  Canton  Unne,  Rolls  Royce,  Hispano- 
Suize,  Hall-Scott,  Mercedes,  Isolta. 

ii6 


AERO   ENGINES 

Stationary  engines  have  their  cylinders  placed  ver- 
tically, V-shaped,  radially,  or  horizontally. 

Magnetos 

The  Bosch  magneto  is  the  most  widely  used  in  the 
air  services.  It  is  driven  either  by  means  of  spur 
wheels  or  chains.  If  the  former  method,  which  is 
usually  adopted,  is  employed,  the  spur  wheels  should 
be  made  alternately  of  hardened  steel  and  phosphor- 
bronze. 

Action  of  the  Magneto 

The  armature  core,  a  soft  laminated  "H"  section, 
is  wound  with  primary  and  secondary  windings;  the 
secondary  is  a  continuation  of  the  primary  and  is 
wound  round  it.  The  primary  is  always  in  series 
with  the  secondary,  and  a  contact-breaker  is  con- 
nected in  series  with  the  primary  and  rotates  bodily 
with  the  armature.  This  armature  rotates  between 
soft  iron  pole  shoes  which  are  magnetized  by  per- 
manent steel  magnets  of  a  horseshoe  shape.  Across 
the  contact-breaker  a  condenser  is  fitted  in  order  to 
eliminate  sparking  at  the  platinum  points  and  to 
insure  a  quick  breaking  of  the  primary  current.  By 
means  of  the  armature  being  rotated  and  the  rotary 
circuit  being  broken  at  the  correct  moment  by  the 
9  "7 


THE  EYES  OF  THE  ARMY  AND  NAVY 

contact-breaker,    a    spark    jumps    across    the    plug 
points. 

Platinum  Points  of  Magnetos 

These  should  be  adjusted  so  that  they  should  not 
break  more  than  0.5  mm.,  and  not  less  than  0.3  mm., 
when  the  fiber  block  strikes  the  steel  segment  on  the 
timing  lever.  These  platinum  points  should  be  care- 
fully and  frequently  examined  and,  if  found  uneven, 
should  be  adjusted  or  replaced  by  new  points. 

High-tension  Terminal 

The  end  of  the  secondary  winding  is  led  out  of  the 
opposite  end  of  the  armature  to  the  end  which  carries 
the  contact-breaker  to  a  slip  ring.  Above  the  ring, 
and  in  contact  with  it,  is  a  carbon  brush  which  is  held 
in  an  ebonite  holder.  From  this  carbon  brush  a  con- 
nection leads  to  the  distributing  wheel  and  thence 
to  the  spark  plugs. 

Low-tension  Terminal 

From  the  low-tension  terminal  a  wire  is  led  to 
the  switch  and  through  this  switch  to  "earth."  When 
a  pilot  desires  to  switch  "on"  the  contact  between 
this  terminal  and  the  earth  is  broken,  and  when  it  is 

118 


AERO   ENGINES 

desired  to  switch  "off"  contact  between  the  terminal 
and  earth  is  made. 


To  Strip  a  Magneto 

First  remove  high-tension  carbon  brush.  Remove 
brass  end  cap  by  turning  spring  round.  Remove 
brass  sleeve  to  which  is  attached  the  switch  terminal. 
Remove  set  screw  which  secures  the  make  and  break. 
This  can  be  done  by  the  means  of  a  screw-driver  being 
placed  beneath  the  brass  disk  and  prizing.  The 
make-and-break  mechanism  will  slide  off  the  spindle 
quite  readily.  Remove  the  four  screws  in  the  end 
plate  adjacent  to  the  timing  wheel.  Remove  the 
armature  and  end  plate.  These  should  come  away 
together  by  prizing  against  the  magnet  poles  with  a 
screw-driver. 

Care  and  Maintenance  of  Aeroplane  Engines 

All  aero  engines  should  run  smoothly,  and  the 
slightest  difference  in  running,  especially  the  presence 
of  metallic  sounds,  should  be  investigated  immedi- 
ately. True  records  of  all  running  time  and  a  state- 
ment of  all  adjustments  of  engines  should  be  logged. 
All  rotary  engines  should  be  thoroughly  overhauled 
after  twenty  to  thirty  hours'  running,  and  stationary 

119 


THE  EYES  OF  THE  ARMY  AND  NAVY 

engines  should  be  thoroughly  overhauled  after  every 
fifty  hours'  running.  In  the  latter  type  the  "piston 
heads  and  plugs  should  be  examined  and  cleaned  after 
every  five  hours'  running  and  the  oil  pump  cleaned 
out  after  every  five  to  six  hours'  running.  When  an 
engine  is  overhauled  a  thorough  examination  for 
cracked  pistons,  valves,  valve  seatings,  piston  rings, 
and  for  flaws  in  the  crankcase  and  connecting  rods 
should  be  made.  Great  care  should  be  taken  that 
the  cylinder  walls,  valve  seatings,  and  all  working 
surfaces  are  protected  from  being  scratched  when 
cleaning  is  in  progress.  Adjustable  bearings  of  en- 
gines should  be  examined  regularly  in  order  to  ascer- 
tain any  signs  of  wear.  In  the  stationary  water- 
cooled  types  rain  or  distilled  water  should  be  used 
to  fill  the  radiators,  and  in  frosty  weather,  unless  the 
sheds  are  heated,  the  radiators  should  be  emptied 
when  the  engine  is  not  in  use. 

Many  types  of  rotary  engines  are  fitted  with  piston 
rings.  These  rings  should  be  removed  with  care 
when  dismantling  an  engine,  and  they  should  be  re- 
placed on  the  piston  from  which  they  were  removed. 

When  "doping"  or  priming  an  engine  care  should 
be  taken  that  the  engine  is  not  over-doped.  A  very 
good  rule  is  to  inject  paraffin  into  the  cylinders  after 
an  engine  has  been  run  for  some  time ;  but  the  engine 
should  be  cool  before  the  paraffin  is  injected.     Rotary 

I20 


AERO    ENGINES 

engines  should  be  rotated  a  few  times  daily  when  not 
in  use,  and  if  the  exhaust  valve  of  the  bottom  cylinder 
is  choked  open  the  excess  oil  will  drain  off. 

All  electrical  connections  should  be  kept  securely 
fastened  and  all  wire  free  from  oil,  moisture,  and 
rust.  Continuous  backfiring  is  detrimental  to  the 
engine  and  should  not  be  permitted. 

The  "mixture"  should  contain,  approximately,  one 
part  of  petrol  to  seventeen  parts  of  air.  In  cold 
weather  less  air  should  be  used.  An  engine  of  any 
description  should  never  be  allowed  to  run  at  the 
maximum  speed.  If  the  maximum  revolutions  of  an 
engine  are  i,8oo  revolutions  per  minute,  1,200  to 
1,300  revolutions  per  minute  would  be  the  speed  at 
which  the  best  results  would  be  obtained.  Use  the 
switch  as  little  as  possible,  thereby  reducing  the 
strains  on  the  engine,  engine-bearers,  and  the  ma- 
chine in  general.  All  engines  deserve  great  care  and 
attention.  See  that  they  get  it  and  the  best  results 
and  a  long  life  of  the  machine  are  assured. 

Causes  for  Defects  of  Engines 

Backfiring.  Spark  too  far  advanced.  Valve  tim- 
ing incorrect.  Broken  inlet  valve  springs.  Sticky 
inlet  valve  stems.  If  self-starting  device  is  fitted, 
backfiring  is  often  caused  by  improper  manipulation. 

121 


THE  EYES  OF  THE  ARMY  AND  NAVY 

Failure  to  Start.  The  main  cause  of  an  engine 
failing  to  start  is  excessive  doping.  To  remedy  this 
fault,  turn  propeller  back  a  few  turns,  cut  off  petrol, 
then  swing  the  propeller  again.  If  the  engine  still 
refuses  to  start,  ascertain  whether  the  magneto  or 
switch  is  out  of  order.  A  good  test  is  by  switching  on 
and  placing  a  finger  on  one  of  the  plugs  of  a  cylinder 
just  previous  to  the  firing-point,  and  by  moving  the 
propeller  backward  and  forward  a  few  times  a  shock 
should  be  felt. 

Pre-ignition.  This  is  mainly  caused  by  over- 
heating, excessive  carbon  deposit,  and  by  having  the 
spark  too  far  advanced. 

Continuation  of  Firing  when  Switch  is  Off. 
Overheated  cylinders,  especially  if  heavily  carbonized. 
Defective  switch,  earth  wire  broken  or  detached  from 
the  magneto  terminal. 

Misfiring.  This  trouble  is  mostly  caused  by  the 
following  magneto  and  switch  troubles:  Magneto 
points  need  adjusting.  Moisture  on  the  high-tension 
terminal  and  wires.  Excess  of  oil  on  the  connecting 
wires.  Carbon  brush  not  bearing  correctly,  owing  to 
weak  spring  or  not  being  in  proper  position  with 
respect  to  the  distributer  ring.  Short  circuit,  caused 
by  dirty,  carbonized,  or  defective  plugs,  or  by  the 
high-tension  wire  coming  into  contact  with  metal 
engine-bearers.     Defective  switch. 

122 


AERO    ENGINES 

Other  causes  of  misfiring  are:  Insufficient  petrol 
supply.  Excessive  petrol  supply.  Needle  valve  not 
correctly  adjusted.  Freezing  of  induction  pipe.  In- 
correct valve  opening  and  closing.  Valve  spring 
broken.  Incorrect  mixture.  Excessive  lack  of  com- 
pression. 

Causes  of  Loss  of  Power.  Loss  of  power  will 
frequently  be  experienced  after  an  engine  has  been 
overhauled,  owing  to  piston  rings,  valves,  and  valve 
seatings  not  having  properly  run  themselves  to  run- 
ning adjustment;  however,  this  remedies  itself  after 
a  short  run.  Insufficient  petrol  supply  or  excessive 
petrol  supply.  Improper  mixture.  Incorrect  valve  or 
ignition  timing.  Defective  valves  or  valve  seatings. 
Cracked  piston  or  seatings.  Overheating  and  lack  or 
excess  of  lubrication.  Excessive  carbon  deposit. 
Misfiring.  Obstructed  inlet  or  exhaust  pipes.  Worn, 
sticky,  or  cracked  piston  rings.  Incorrect  placing  of 
engine  in  the  aeroplane.  Improper  adjustment  of 
bearings.  Worn  valve  guides,  cams,  rollers,  or 
valve-rod  pins.  Defective  inlet  or  broken  exhaust 
valve  springs.  Excessive  vibrations,  due  either  to 
unbalanced  engine  or  unbalanced  propeller,  unequal 
tension  in  inlet-valve  springs,  or  weak  engine-bearers 
will  cause  great  loss  of  power. 


123 


THE  EYES  OF  THE  ARMY  AND  NAVY 

Lubricants 

In  all  lubricants  for  aero  engines  the  flash  point 
should  be  high.  Lubricants  containing  mineral  prop- 
erties are  used  for  the  majority  of  stationary  engines 
and  castor-oil  for  all  rotary  engines.  The  evaporation 
of  petrol  causes  a  distinct  lowering  of  temperature, 
and  all  lubricating  oils  should  have  qualities  in  order 
to  withstand  the  low  temperature  without  liability 
to  congeal.  They  should  also  contain  such  proper- 
ties that  high  temperatures  will  not  decrease  their 
viscosity.  When  exposed  to  heat  no  acids  or  cor- 
rosive fluids  should  be  formed.  Oils  that  have  prop- 
erties that  make  them  liable  to  gum  or  to  set  up  ex- 
cessive carbon  should  be  avoided. 

System  of  Oiling  on  Rotary  Engines 

Castor-oil  is  used  for  all  rotary  engines  because  it 
does  not  mix  with  petrol.  In  all  the  gnome  types, 
except  the  double-cylinder  ones,  only  one  oil  pump 
is  fitted.  All  high-powered  rotaries  are  fitted  with 
two  oil  pumps.  The  oil  flows  to  the  pump  by  gravity 
and  a  pinion  wheel  operates  the  pump.  This  con- 
sists of  two  plungers  and  two  piston  valves.  The  oil 
is  forced  along  two  copper  tubes  to  the  hollow  crank- 
shaft, where  two  internal  copper  pipes  lead  part  of 

124 


AERO    ENGINES 

the  supply  to  the  thrust  bearings  and  the  other  part 
to  the  crank  pin.  From  the  pin  it  travels  along  the 
connecting  rods  to  the  gudgeon  pins  and  then  through 
small  holes  in  the  top  angle  of  the  piston,  and  so 
lubricates  the  cylinders.  The  oil  pump  should  be 
cleaned  regularly  and  special  attention  paid  to  the 
suction  holes. 

Carburetor 

The  carburetor  is  that  part  of  an  engine  which  is 
responsible  for  the  regular  supply  of  "mixture." 
There  are  many  types  of  carburetors  and  many 
methods  of  carburation,  but  the  main  principle  in 
all  of  them  is  similar.  The  petrol  is  led  from  the 
petrol  tank,  either  by  means  of  gravity  or  pressure, 
to  the  "float  chamber."  This  chamber  keeps  the 
petrol  at  a  constant  level  and  prevents  the  carburetor 
from  overflowing  when  the  engine  is  throttled  down 
or  when  the  engine  is  not  running.  Inside  this  float 
chamber  is  a  brass  float  and  through  this  float  a 
needle  valve  passes.  When  the  float  has  risen  to  a 
certain  position  the  top  of  the  float  comes  into  con- 
tact with  two  balance  weights,  which  are  pivoted  about 
the  needle,  and  when  these  weights  are  forced  up 
the  needle  is  forced  down  and  the  bottom  of  the 
needle  valve  falls  down  into  the  supply  jet,  and  by 
doing  so  cuts  off  the  supply  of  petrol.     When  the 

125 


THE  EYES  OF  THE  ARMY  AND  NAVY 

level  of  the  petrol  falls  the  float  falls,  the  weights  are 
released  and  drop,  and  the  needle  valve  is  forced  up, 
allowing  a  fresh  supply  of  petrol  to  pass  into  the 
chamber.  By  means  of  lifting  the  needle  valve  the 
carburetor  can  be  flooded  in  order  to  start  the  engine. 
A  small  pipe  leads  the  petrol  from  the  float  chamber 
into  the  jet  chamber.  A  vertical  jet  or  nozzle  is 
attached  to  the  end  of  this  pipe.  Around  this  jet  a 
partial  vacuum,  due  to  the^  suction  effect  of  the  en- 
gine, is  set  up  and  the  petrol  is  emitted  in  a  fine 
spray.  This  spray  is  evaporized  easily  and  conse- 
quently mixed  with  the  air,  being  sucked  past  the  jet. 
Some  types  of  carburetors  are  fitted  with  an  arrange- 
ment for  warming  the  supply  of  air  to  the  carburetor 
and  thereby  assisting  evaporization.  From  the  jet 
chamber  the  mixture  passes  along  the  induction  pipe 
to  the  cylinder. 


X 

AEROPLANE    AND   AIRSHIP   INSTRUMENTS 

ALL  aeroplane  and  airship  instruments  are  very 
,  delicate ;  they  are  easily  damaged  and  are  costly 
to  repair.  Great  care  should  be  taken  in  handling 
them  and  at  all  times  they  should  be  protected  from 
oil,  dirt,  and  dust. 

Altimeter 

It  has  been  stated  that  as  height  is  attained  the  pres- 
sure of  the  atmosphere  decreases.  The  approximate 
decrease,  relative  to  the  height,  is  i°  in  every  275  feet; 
therefore  an  instrument  which  is  affected  by  the  pres- 
sure of  the  atmosphere  will  give  a  rough  indication 
of  the  height.  The  altimeter  is  an  aneroid  barometer, 
graduated  in  hundreds  of  feet,  and  is  designed  to  show 
height  instead  of  pressure.  Altimeters  are  made  in  all 
sizes,  from  the  size  of  a  watch  to  a  dial  ten  inches  in 
diameter.  This  instrument  is  operated  by  means  of  a 
corrugated  metal  vacuum  drum.  As  the  pressure  of 
the  air  decreases  or  increases  the  metal  drum  rises  or 

127 


THE  EYES  OF  THE  ARMY  AND  NAVY 

falls,  respectively,  and  these  movements  are  commu- 
nicated to  a  pointer  moving  over  a  graduated  scale. 
Care  should  be  taken  that  the  altimeter  is  set  at  the 
"zero"  mark  on  the  ground,  before  a  flight  is  under- 
taken; the  pressure  of  the  atmosphere  varies  daily 
and  it  frequently  acts  upon  the  instrument  at  the 
earth's  surface. 

Anemometer 

This  is  an  instrument  for  measuring  the  force  or 
velocity  of  the  wind  at  the  earth's  surface.  There  are 
many  types  of  anemometers,  but  the  one  favored  in 
the  air  services  is  the  "cup  operated."  By  means  of 
four  or  more  out-facing  cups  mounted  on  a  revolving 
spindle  the  velocity  of  the  wind  is  ascertained  by  a 
count  of  the  revolutions  applied  to  a  scale. 

Aneroid  Barometer 

This  is  an  instrument  for  determining  the  pressure 
of  the  atmosphere.  The  operation  of  this  instrument 
is  very  similar  to  the  operation  of  the  altimeter.  It 
registers  the  pressure  of  the  atmosphere  instead  of  a 
rough  estimation  of  the  height. 

Inclinometer 

This  instrument  is  of  the  same  principle  as  the  ordi- 
nary spirit-level,  but  is  placed  vertically  in  the  ma- 

128 


AEROPLANE    INSTRUMENTS 

chine  so  as  to  indicate,  in  degrees,  any  slight  change 
in  angle  of  the  fore-and-aft  line  of  the  aeroplane  or 
airship.  Zero,  or  level,  is  the  flying-level  position  of  the 
aircraft.  This  instrument,  as  also  the  laterometer, 
should  be  rigidly  attached  to  the  machine,  and  if 
placed  correctly  should  never  require  a(i justing. 

Laterometer 

This  instrument  is  also  similar  to  the  ordinary  spirit- 
level.  It  is  set  in  the  machine  horizontally  to  indicate 
any  change  of  angle  in  the  lateral  position  of  the  air- 
craft. This  instrument  is  so  constructed  that  when 
a  turn  is  being  made,  zero  will  be  registered;  that  is, 
if  there  is  no  "side  slip."  But  if  a  turn  without 
"bank  "  is  attempted,  the  side  slip,  which  would  occur, 
would  be  registered  immediately  by  this  instrument. 

Pressure-gauge 

This  instrument  is  used  for  registering  the  difference 
between  the  pressure  of  the  gas  or  air  in  the  envelope 
of  an  airship  and  the  pressure  of  the  outside  atmos- 
phere. The  favorite  type  is  the  "  U  "  tube.  The  tube 
is  made  of  glass  and  is  half  filled  with  colored  liquid. 
A  scale  is  graduated  on  either  side  of  the  tube  and 
divided  into  millimetres.    The  tube  that  leads  to  the 

129 


THE  EYES  OF  THE  ARMY  AND  NAVY 

envelope  has  the  scale  reading  from  zero  to  zenith 
down  the  tube;  the  connected  tube  exposed  to  the 
atmosphere  has  the  scale  reading  from  zero  to  zenith 
up  the  tube.  When  the  pressure  in  the  envelope  of 
the  airship  and  that  of  the  atmosphere  are  equal,  both 
scales  should  read  zero.  If  the  liquid  in  the  tube,  con- 
nected to  the  gas-bag,  is  lower,  or  reads  lower  than  the 
atmospheric-pressure  scale,  it  is  readily  observed  that 
the  pressure  of  the  gas  or  air  is  greater,  and  vice  versa. 
In  many  of  the  latest  types  of  pressure-gauges  one  arm 
of  the  "U"  tube  is  somewhat  thicker  than  the  other, 
in  order  to  insure  a  quicker  and  more  accurate  reading. 

Manometer 

This  is  another  type  of  pressure-gauge.  Its  princi- 
ple is  similar  to  that  of  the  aneroid,  but  far  more 
delicate,  and  records  the  pressure  of  the  gas  in  milU- 
metres  of  water. 

Revolution-counter 

This  instrument  is  for  ascertaining  the  revolutions 
of  the  engine.  It  is  operated  by  means  of  a  governor. 
A  cable  is  led  from  a  worm  wheel  on  the  engine  to  the 
revolution-counter  box;  increase  of  the  revolutions 
of  the  cable  forces  the  balls  of  the  governor  to  swing 
out ;  this  in  turn  forces  the  pivot  of  the  governor  down. 
In  a  similar  manner,  if  there  is  a  decrease  of  revolutions 

130 


AEROPLANE    INSTRUMENTS 

of  the  cable,  the  balls  of  the  governor,  owing  to  their 
weight,  will  drop  and  force  the  pivot  up.  These 
movements  are  communicated  to  a  pointer  which  reg- 
isters the  reading. 

Speed-indicator 

The  function  of  this  instrument  is  to  register  the 
speed  of  a  machine  through  the  air,  not  the  speed 
of  the  machine  in  relation  to  the  ground.  Ground 
speed  is  estimated  by  adding  the  wind  velocity  to  or 
subtracting  it  from  the  air  speed.  The  speed-indicator 
is  operated  by  means  of  a  leather  diaphragm.  Two 
tubes,  the  pitdt  and  the  static  tube,  are  placed  at  the 
leading  edge  of  the  machine,  openings  facing  toward 
the  direction  of  motion,  and  are  connected  to  the 
instrument.  The  pitot  tube  is  left  full  open  at  the 
end,  and  allows  the  wind  to  pass  down  the  tube  to  the 
instrument.  The  static  tube  has  a  small  cone  attached 
to  its  end,  and  this  cone  overlaps  part  of  the  tube. 
The  wind  passing  over  the  cone  causes  a  negative  pres- 
sure or  suction  to  be  set  up  at  the  overlapping  point. 
Through  small  holes  in  the  tube  at  this  point  the 
suction  force  continues  along  the  tube  to  the  instru- 
ment. The  box  of  the  instrument  is  divided  into 
two  distinct  chambers  by  means  of  a  leather  dia- 
phragm. On  one  side  of  this  diaphragm  the  pitot 
tube  enters,  and  on  the  other  side  of  the  diaphragm 

131 


THE  EYES  OF  THE  ARMY  AND  NAVY 

the  static  tube  enters  the  box  of  the  revolution- 
counter.  The  increase  of  pressure  in  the  one  cham- 
ber, caused  by  the  wind  blowing  down  the  pitot  tube, 
and  the  decrease  of  pressure  in  the  other  chamber, 
caused  by  the  suction  in  the  static  tube,  cause  the 
diaphragm  to  move  accordingly.  To  the  center  of 
the  diaphragm  a  needle  is  attached,  and  this  needle 
is  free  to  move  backward  or  forward,  according  to 
the  movements  of  the  diaphragm.  This  needle  com- 
municates all  movements  to  a  small  lever,  and  in 
conjunction  with  a  fine  spring  gives  movement  to  a 
pointer  on  a  graduated  scale  and  so  registers  the  air 
speed  of  the  aircraft.  The  two  tubes  are  always 
placed  together  and  should  be  placed  in  a  position 
of  least  disturbance  from  the  revolutions  of  the  pro- 
peller and  from  the  eddies  set  up  at  the  wing-tip. 
About  half-way  along  the  wing,  and  on  the  leading 
edge  of  the  upper  plane,  is  the  usual  and  the  best 
position.  In  an  airship  they  should  be  placed  on  the 
framework,  well  forward  and  away  from  aE  disturbing 

influences. 

Statoscope 

An  instrument  designed  to  register  the  difference 
of  atmospheric  pressure  at  heights  varying  by  only 
a  few  feet  and  so  to  detect  whether  an  aircraft  is 
rising  or  falling. 


XI 

WIRELESS    TELEGRAPHY    AND    SEMAPHORE 

Importance 

EVERY  pilot  should  have  a  knowledge  of  the 
elementary  principles  of  wireless  telegraphy;  he 
should  be  able  to  read  Morse,  to  send  at  least  ten 
words  a  minute,  and  should  know  how  to  semaphore. 
It  may  seem  absurd  to  many  pilots  to  study  these 
subjects,  but  some  day,  sooner  or  later,  if  a  person 
continues  flying,  the  need  and  usefulness  of  these  sub- 
jects will  be  realized.  For  instance,  a  pilot  on  sea- 
plane duty  has  a  forced  landing.  A  passing  vessel 
signals,  asking  him  if  he  requires  help.  If  he  has  a 
knowledge  of  semaphore  he  will  be  able  to  communi- 
cate with  the  vessel,  whereas  if  he  is  unable  to  read 
or  send  semaphore  he  might  be  ignored  by  the  passing 
vessel  and  be  at  the  mercy  of  the  elements  for  many 
days  before  another  vessel  is  sighted.  When  on 
active  service  it  often  happens  that  observers  are 
scarce  and  a  pilot  may  be  ordered  to  act  as  an  ob- 
lo  133 


THE  EYES  OF  THE  ARMY  AND  NAVY 

server  on  an  expedition  over  the  enemy's  lines.  Cn 
such  an  occasion  a  knowledge  of  wireless  would  be 
invaluable. 

In  graduating  as  a  pilot  in  the  air  services  there 
is  always  an  examination  on  elementary  wireless, 
and  a  pilot  is  required  to  read  ten  words  a 
minute  and  to  send  eight  words  a  minute  in  wireless 
and  semaphore. 


Elementary  Principles  of  Wireless 

To  describe  fully  the  elementary  principles  of 
wireless  telegraphy  would  require  from  one  hun- 
dred to  one  hundred  and  fifty  of  these  pages,  and 
would  be  out  of  place  in  a  work  of  this  descrip- 
tion. In  this  article  a  short  description  of  the 
fundamental  principles,  the  symbols  used,  and  the 
Morse  and  Phillips  codes  are  given.  This  covers  all 
that  is  required  to  be  known  by  the  pilot,  for  all 
practical  purposes. 

Careful  methodical  study  and  drill  on  the  practical 
application  of  the  various  symbols  on  the  instruments 
is  required  to  master  the  art  of  good  sending  and 
receiving.  In  the  actual  study  the  first  step  is  to 
memorize  the  alphabet  numerals  and  practical  punc- 
tuation code. 

134 


The  Morse  Code 


A           B 

C 

D 

E          F 

G 

H 

I            J 

K 

L 

M        N 

0 

P 

Q 

R 

S 

T         U 

V 

W 

X 

Y 

Z 

I 

2 

3 

4 

S 

6 

78  90 

Comma, Period,  -  -    -  -    -  - 

Practical  Symbols  of  the  Phillips  Code  (American) 
A  B  CDEF  G  HI 

J  K  LMNOP  Q 

RSTU  V  WXY 

Z  & 

I  23456 

78  90 


Period  . Comma  , —      Interrogation  mark  ? 


THE  EYES  OF  THE  ARMY  AND  NAVY 


Units  of  Electricity 

In  order  to  define  and  measure  the  various  electrical 
factors  of  a  circuit  certain  practical  standards,  or 
units,  have  been  adopted. 


The  unit  of  quality 

"  "  "  current 

"  "  "  power 

"  "  "  energy 

"  "  "  capacity 

"  "  "  inductance 

**  "  "  resistance 


is  one  coulomb 

"  ampere 

"  watt 

"  joule 

*'  farad 

"  henry 

"  ohm 


"  pressure  or  electromotive  force 
is  one  volt 


The  Coulomb 

The  coulomb  can  be  compared  with  the  "gallon" 
or  the  mechanical  unit  of  an  engine — namely,  "one 
revolution." 

The  Ampere 

This  unit  can  be  compared  with  the  number  of 
"gallons  per  second"  that  are  flowing  in  a  water- 
main,  or  the  number  of  "revolutions  per  minute"  of 
an  engine. 

The  Watt 

The  rate  of  doing  work.  One  watt  is  ti: :  power 
required  to  do  one  joule  of  work  per  second. 

Watt  =  volts  +  amperes 
136 


WIRELESS    AND    SEMAPHORE 

For  convenience,  the  kilowatt  is  often  used  as  the 
unit  of  electrical  power  instead  of  the  watt.  One 
kilowatt  is  equal  to  i,ooo  watts. 

The  Joule 

In  order  to  cause  a  current  of  electricity  to  flow  in 
a  circuit,  energy  or  work  must  be  expended,  and  the 
joule  is  the  unit  of  electrical  energy  or  work. 

The  Farad 

The  farad  is  the  unit  of  capacity.  This  unit  is  a 
large  one,  and  for  convenience  the  microfarad,  a 
millionth  part  of  a  farad,  is  usually  adopted. 

The  Henry 

This  is  the  unit  of  inductance.  This  term  induct- 
ance should  not  be  confused  with  the  term  resistance. 
Resistance  opposes  a  flow  of  electricity.  Inductance  is 
best  described  as  "inertia."  It  is  well  known  that 
when  an  engine  with  a  heavy  fly-wheel  is  started  a 
short  time  elapses  before  the  engine  has  attained  full 
speed,  owing  to  the  "inertia"  of  the  heavy  fly-wheel. 
In  a  similar  manner  inductance  is  the  quality  in  a  cur- 
rent which  tends  to  oppose  any  change  in  the  flow  of 

137 


VAMABLE 
RESISTANCE 


INDUCTIVE 
WINDING 


VARIABLE 
INDUCTANCE 


TWO  COILS  HAVING 
MUTUAL   INDUCTANCE 


RESISTANCE 
COIL 


CONDUCTORS 
CROSSING 


f- 


\^ 


POSITIVE 


BATTERY 


SWITCH  NEGATIVE 

SYMBOLS  USED  IN  DIAGRAMS  OF  WIRELESS-TELEGRAPHY  CIRCUITS 


.CONDUCTOR 


CONDUCTORS 
CONNECTED 


CONDENSER 


w 


ZZL 


/ 


VARIABLE 
CONDENSER 


JoL 


CRYSTAL 
DETECTOR 


DIRECT-CURRENT 
DYNAMO 


4- 


F 


CELLS 


ALTERNATING 
CURRENT 


— O       Q— 

— D     a— 

SPARK  GAPS 


SYMBOLS  USED  IN  DIAGRAMS  OF  WIRELESS-TELEGRAPHY  CIRCUITS 


The  eyes  of  the  army  and  navy 

capacity.  The  microhenry  is  frequently  used  as  a 
unit.  One  microhenry  is  equal  to  one  millionth  part 
of  a  henry. 

The  Ohm 

The  ohm  is  the  unit  of  resistance.  Just  as  friction 
opposes  the  flow  of  water  through  a  pipe,  so  does 
resistance  oppose  the  flow  of  electricity  through  a  con- 
ductor. 

The  Volt 

The  volt  is  the  unit  of  electrical  pressure.  It  can  be 
compared  with  the  practical  unit  of  mechanical  force — 
namely,  the  pound.  For  instance,  a  flow  of  water — 
that  is,  the  number  of  gallons  per  hour  that  will  flow 
through  a  pipe  of  given  length,  size,  and  shape — will 
depend  upon  the  number  of  pounds  of  pressure  applied 
behind  the  water. 

Magnetism 

The  power  which  a  magnet  has  of  attracting  iron 
or  any  other  magnetic  substance  is  termed  magnetism. 
When  a  piece  of  steel  is  magnetized  it  is  called  a  per- 
manent magnet.  One  end  of  this  magnet  would  be 
termed  the  north  pole,  and  the  opposite  end  the  south 
pole.  The  range  of  any  space  over  which  the  magnet 
will  attract  other  magnetic  substances  is  called  the 

140 


WIRELESS    AND    SEMAPHORE 

magnetic  field.  Like  poles  repel,  and  unlike  poles 
attract  one  another.  For  instance,  if  the  north  pole 
of  one  magnet  is  brought  near  the  south  pole  of  an- 
other magnet  the  two  will  attract  each  other,  and  if 
the  two  north  poles  or  two  south  poles  are  brought 
together  they  will  repel  each  other.  The  "lines  of 
force"  pass  out  from  the  north  pole  of  a  magnet, 
round  a  circuit,  and  return  into  the  south  pole.  Any- 
magnetic  substance  which  is  brought  into  the  magnetic 
field  of  a  magnet  becomes  magnetized.  This  effect 
is  termed  "magnetic  inductance." 

It  should  be  borne  in  mind  that  magnetism  is  not 
electricity.  The  study  of  the  relation  between  the 
two  forces  is  called  "electromagnetism." 

Electromagnetism 

A  magnetic  field  is  produced  around  a  conductor 
when  an  electric  current  is  passed  through  the  con- 
ductor. A  field  of  this  description  consists  of  a  num- 
ber of  lines  of  force  in  concentric  circles  traveling 
around  the  conductor.  The  direction  of  these  lines 
of  force  is  influenced  by  the  direction  of  the  current. 
If  a  conductor  is  bent  so  as  to  form  a  coil,  it  will  be 
readily  observed  that  the  lines  of  force  will  act  upward 
on  the  inside  of  the  coil  and  in  a  downward  direction 
on  the  outside  of  the  coil;   but  instead  of  the  lines  of 

141 


THE  EYES  OF  THE  ARMY  AND  NAVY 

force  acting  right  round  one  turn  of  the  wire,  they 
combine  with  those  produced  by  the  next  turn  and 
form  complete  Hnes  of  force,  as  shown  in  Fig.  37. 

In  this  way  a  bobbin  or  coil  of  wire  is  very  similar 
to  a  magnet.    If  a  steel  rod  is  placed  in  the  center  of 


I'll     I    ^S^TT^n/   ^  . V \    \ 


\\\\\ 


lllll'  l> 

t    I    J   f 


"^m^ 


Fig.ar 

the  bobbin  or  coil  it  will  become  a  permanent  magnet ; 
if  a  rod  of  soft  iron  is  inserted  into  the  coil  it  becomes 
a  magnet,  but  not  a  permanent  magnet,  because  the 
magnetism  only  lasts  as  long  as  the  current  lasts. 
A  magnet  of  this  latter  description  is  called  an  electro- 
magnet. If  the  two  ends  of  the  wire  around  the  coil  are 
joined  a  current  of  electricity  will  flow  through  the 
coil.  This  effect  is  known  as  electromagnet  induction. 
The  strength  of  the  current  induced  will  depend  upon 

142 


WIRELESS    AND    SEMAPHORE 

the  rate  of  change  in  the  number  of  magnetic  lines  of 
force  passing  through  the  coil. 

Mutual  Induction 

It  has  already  been  stated  that  if  an  electric  current 
is  passed  through  a  coil  of  wire,  a  magnetic  field, 
similar  to  that  produced  by  a  permanent  magnet, 
would  result.  Now  instead  of  placing  a  steel  rod  or 
soft  iron  rod  inside  a  coil,  a  smaller  coil  of  wire  may 
take  the  place  of  the  rod  of  steel  or  iron,  and  if  a  cur- 
rent of  electricity  is  kept  flowing  through  the  smaller 
coil  it  is  termed  "mutual  induction."  In  this  method 
the  smaller  coil  is  termed  the  primary  coil  and  the 
larger  coil  the  secondary  coil.  It  will  be  readily  ob- 
served that  if  a  core  of  iron  is  passed  through  the 
primary  coil  the  voltage  of  the  secondary  coil  will  be 
greatly  increased.  In  the  case  of  mutual  induction  it 
is  not  necessary  to  move  the  primary  coil  in  and  out 
of  the  secondary  coil  in  order  to  change  the  number 
of  lines  of  force.  This  is  done  by  the  switch  connecting 
the  circuit  at  the  ends  of  the  primary  coil. 

The  Condenser 

The  function  of  the  condenser  is  holding  an  electrical 
charge  and  exerting  an  opposite  force.     One  simple 

143 


THE  EYES  OF  THE  ARMY  AND  NAVY 

type  of  condenser  consists  of  a  plate  of  glass  covered 
with  tin-foil, .  or  any  other  thin  conductor,  on  both 
sides.    This  conductor  merely  acts  as  a  means  of  dis- 


-h 


Battery 


Fig.38 

tributing  any  applied  electrical  pressure   uniformly 
over  the  surface  of  the  dielectric,  or  non-conductor. 


The  Circuit 

A  circuit  is  a  path  composed  of  a  conductor,  or 
conductors,  through  which  an  electric  current  flows 
from  one  point  in  it,  around  the  conducting  path 
and  back  to  the  point  from  which  it  started.  Vari- 
ous parts  of  the  circuit  may  be  connected,  either 
in  series  or  in  parallel.  (Figs.  38  and  39.)  For 
instance,  when  two  conductors,  H  and  O,  are  joined 

144 


WIRELESS    AND    SEMAPHORE 

together  as  illustrated  in  Fig.  38  they  are  said  to 
be  joined  in  parallel,  and  if  joined  as  shown  in  Fig, 
39  they  are  said  to  be  joined  in  series.  In  the  former 
method  only  a  portion  of  the  total  current  passes 


through  each  conductor,  and  in  the  latter  method 
the  whole  current  passes  through  each  conductor 
successively. 

Cells 

Cells  are  a  source  of  electrical  pressure  obtained 
from  chemical  action.  Cells  may  also  be  connected 
in  parallel  or  series,  and  the  same  principle,  regarding 
the  flow  of  current,  applies  as  described  above. 


Accumulators 

An  accumulator  is  a  cell  in  which,  if  a  current  of 
electricity  is  passed  through,  chemical  action  is  set 

145 


THE  EYES  OF  THE  ARMY  AND  NAVY 

up  between  two  plates  in  the  cell  and  the  electrolyte 
surrounding  them.  This  is  known  as  charging  the 
cells,  and  the  current  is  known  as  the  charging  current. 
When  this  current  is  discontinued  and  the  two  plates 
are  joined  together,  the  cell  will  act  the  same  way  as 
a  primary  cell  and  a  current  of  electricity  will  pass 
from  the  cell  through  the  conductor  in  a  direction  op- 
posite to  that  of  the  charging  ciurent.  When  two  or 
more  accumulators  are  joined  together  they  are 
termed  an  accumulator  battery. 

Electric  Waves 

In  order  to  communicate  between  one  point  and 
another  point  by  wireless  telegraphy  it  is  necessary  to 
have  an  apparatus  for  producing  and  emitting  electric 
waves  at  the  one  point,  and  an  apparatus  for  detecting 
them  at  the  other  point.  The  aerial  wire  performs 
both  functions  at  each  point.  A  charge  of  electricity 
is  sent  into  the  aerial  wire  by  a  movement  of  the  key. 
The  current  will  be  large  at  first  and  will  gradually 
diminish  as  the  aerial  becomes  charged.  When  the 
aerial  becomes  fully  charged  the  current  will  cease  to 
flow  in  the  direction  in  which  the  current  traveled 
and  will  flow  in  the  opposite  direction.  By  movements 
of  the  key  the  current  is  despatched  backward  and 
forward  and  is  termed  an  oscillating  current. 

146 


WIRELESS    AND    SEMAPHORE 

Wave  lengths,  usually  employed  in  wireless,  vary 
in  length  from  loo  metres  to  over  15,000  metres.  The 
larger  the  power  of  a  station  the  longer  the  wave 
length  employed.  However,  if  the  length  of  an  aerial 
is  increased,  the  capacity  and  induction  of  the  aerial 
is  increased,  and  thereby  the  fundamental  wave  length 
is  also  increased. 

The  Aerial 

It  is  often  necessary  to  adjust  the  aerial  to  obtain 
the  desired  electric  wave  length,  and  in  aerial — that 
is,  aeroplane — wireless  this  is  frequently  done  by  let- 
ting out  or  taking  in  the  aerial  wire,  although  most  of 
the  latest  types  of  wireless  outfits  are  fitted  with  a 
special  apparatus  for  increasing  or  decreasing  the 
wave  length  without  altering  the  aerial  wire. 

It  is  obvious  that  the  aerial  circuit  has  to  be  "in 
tune"  for  despatching  a  signal,  and  must  also  be  in 
tune  for  receiving  a  signal.  The  buzzer  must  also  be 
adjusted  and  in  tune  for  the  two  circuits,  the  oscilla- 
tory circuit  and  the  generating  circuit  by  which  the 
oscillatory  is  excited. 

When  at  semaphore  drill  or  actually  sending  mes- 
sages, the  following  points  are  important: 

The  signaler  should  stand  exactly  facing  the  oppo- 
site person  or  station. 

The  flags  must  not  be  thrown  to  the  rear,  and  should 

147 


THE  EYES  OF  THE  ARMY  AND  NAVY 


be  held  at  the  full  extent  of  the  arms  and  in  exact 
prolongation  of  them. 

Care  should  be  taken  that  the  arms  are  placed  at  the 
exact  position  to  indicate  the  letters  and  signs. 

When  making  the  letters  T,  O,  W,  and  the  numeral 
sign,  the  flags  should  be  distinctly  separated,  not 
crossing  each  other. 

The  signaler  should  turn  slightly  on  the  hips  when 
making  letters  such  as  J,  X,  O,  Z,  but  the  eyes  of  the 
signaler  should  continue  to  look  straight  to  the  front. 

When  double  letters  occur,  the  flags  should  be 
brought  in  to  the  body  after  the  first  letter  is  made. 

The  flags  should  be  kept  unfurled  and  moved  quickly 
from  one  letter  or  sign  to  the  next.  A  pause  should 
be  made  on  the  letter  or  sign,  according  to  the  rate  of 
sending. 

The  simplest  method  of  learning  the  semaphore 
alphabet  and  signs  is  by  circles,  thus: 

First  circle,  A  to  G 

Second  circle,  H  to  N  (omitting  J) 

Third  circle,  O  to  S 

Fourth    circle,    T,    U,    Y,    and 
"Erase" 

Fifth  circle,  Numerical  sign,  J  (or 
Alphabetical  sign),  and  V 

Sixth  circle,  W  and  X 
Seventh  circle,  Z 
148 


Fig.  40 


WIRELESS    AND    SEMAPHORE 

In  the  first  circle,  the  letters  A  to  D  should  be  made 
with  the  right  arm,  and  E  to  G  with  the  left  arm. 

When  semaphoring  without  the  use  of  flags  the  arms 
should  be  placed  in  a  correct  position,  and  in  making 
letters  where  only  one  arm  is  used,  that  arm  should 
not  be  brought  across  the  body. 

When  letters  follow  one  another,  as  in  a  word  or 
group,  the  flags  should  not  be  brought  back  to  the 
"ready"  position  after  each  letter,  but  if  an  arm  is 
already  in  position  to  form  or  to  assist  to  form  the 
next,  it  should  be  kept  steady. 

When  sending  words  and  groups,  the  arms  must  be 
moved  from  letter  to  letter  and  both  arms  brought 
in  to  the  non-signaling  position  on  completion  of  the 
word  or  group. 

The  caller  and  writer  should  stand  immediately  in 
rear  of  the  sender  and  reader,  respectively,  so  that  they 
may  be  clear  of  the  flags  and  yet  close  enough  to  be 
heard  and  to  hear  the  latter  distinctly. 

The  same  signs  are  used  for  the  numerals  i  to  o  as 
for  the  letters  A  to  K  (omitting  J),  but  are  distin- 
guished from  the  latter  by  being  preceded  by  the 
"numerical  sign"  and  followed  by  the  "alphabetical 
sign."     They  are  checked  by  being  repeated  back. 

The  "Stop"  signal  is  "PP." 

The  "General  Answer"  will  be  made  by  the  letter 
A  or  T,  and  "Flag  up  "  by  the  letter  E. 

II  149 


i 


mn& 


t 


Ready  ^ 

Numerical  Sign 


\ 


E 


Erase  ^ 

Alphabetical  Sign 


SEMAPHORE  ALPHABET   AND   NUMERAL   SIGNS 


WIRELESS    AND    SEMAPHORE 

The  "Preparative"  is  J  and  waving  the  flags,  and 
is  answered  by  the  "General  Answer." 

Known  stations  are  called  up  and  answer  by  their 
station  calls;  unknown  stations  by  the  "Preparative" 
and  answer  by  the  "General  Answer." 

The  "Erase"  (opposite  to  L)  is  used  (a)  to  erase  a 
word  or  group  sent  incorrectly,  or  (6)  to  erase  a  word 
or  group  incorrectly  checked. 

Go  on,  or  spell  out,  is  signaled  G. 

The  "Repeat"  signal  is  I  M  I. 

"Word  after"  is  signaled  W  A. 

"Word  before"  is  signaled  W  B. 

"End  of  message"  is  signaled  V  E. 

"Message  correct"  is  signaled  R  D. 

The  "Obliterator"  sign  is  W  W. 

The  "numerical"  sign  (opposite  to  T)  will  be  used 
to  indicate  numerals  about  to  be  sent,  and  the  "alpha- 
betical" sign  to  indicate  numerals  finished,  letters 
being  resumed. 


XII 

AERIAL   PHOTOGRAPHY 

A  ERIAL  photography  is  a  very  important  branch 
l\  of  duty  carried  out  by  the  air  services.  It  differs 
greatly  from  photography  on  the  ground.  It  is  put 
to  a  variety  of  uses.  Where  objects  are  easy  to  ob- 
serve and  count,  it  is  not  of  much  assistance,  but  a 
photographic  record  of  defended  harbors,  arsenals, 
coast-works  and  dockyards,  giving  their  relative 
position  with  objects  visible  from  the  sea,  is  of 
valuable  importance  to  attacking  ships.  Aeroplanes 
operating  with  the  land  forces  have  a  much  wider 
scope  for  their  activities,  and  an  extensive  list  of  the 
uses  of  aerial  photography  may  be  found  in  military 
manuals. 

It  requires  much  study  combined  with  actual  ex- 
perience and  practical  experiments  to  become  an  ex- 
pert photographer.  To  go  into  the  subject  thorough- 
ly, in  this  handbook,  would  be  out  of  place.  This 
chapter  is  intended  for  those  who  wish  to  acquire 
sufficient  knowledge  of  the  subject  to  enable  them  to 

152 


AERIAL    PHOTOGRAPHY 

take  successful  photographs,  from  an  amateur's 
point  of  view;  however,  a  few  notes  have  been  added 
that  may  be  found  useful  for  reference  purposes  by 
aerial  photographers  detailed  for  official  work. 

Camera 

Any  good  camera  may  be  used  for  aeronautical 
work,  but  to  obtain  the  best  results  the  following 
points  should  be  observed :  The  lens  should  be  of  the 
very  best  quality,  and  a  large  aperture  lens  is  essen- 
tial. The  largest  possible  aperture  enables  the  fast- 
est possible  exposure.  A  large  aperture  is  advised 
for  all  exposures  and  at  all  times.  The  majority  of 
service  photographers  set  thpir  lenses  at  the  maximum 
aperture  and  never,  on  any  occasion"  reduce  them. 
If  the  light  is  bright  the  time  of  exposure  is  reduced, 
instead  of  the  size  of  the  aperture.  Most  aeronautical 
photographs  are  taken  at  a  medium  height,  but  on 
active  service  some  are  occasionally  taken  at  a  great 
elevation.  The  height  at  which  a  photograph  is 
taken  depends,  largely,  on  the  size  of  the  field  and 
the  amount  of  detail  required.  The  usual  elevation 
at  which  service  pictures  are  taken  is  from  6,500  to 
9,000  feet. 

Focus  Lens 

As  a  wide  field  is  generally  required  when  taking 
pictures  from  a  height,  a  short  focus  lens  is  advisable. 

553 


THE  EYES  OF  THE  ARMY  AND  NAVY 

If  details  are  wanted,  an  enlargement  can  be  made. 
When  taking  photographs  for  ofBcial  information  it 
is  not  wise  to  use  a  shorter  focus  than  a  6-inch,  or 
the  detail  becomes  altogether  too  small.  With  a 
half-plate  camera  a  6-inch  lens  is  very  satisfactory. 

Ultra-violet  Rays 

There  is  ever  present  between  the  aircraft  and  the 
ground  a  mass  of  air  carrying  dust  particles  and  mois- 
ture, which  have  the  properties  of  reflecting  the  blue 
light  in  the  atmosphere.  These  dust  particles  cause 
a  bluish-violet  haze  to  appear  above  the  ground  when- 
ever the  sky  is  clear.  This  haze  varies  in  density. 
When  the  sky  is  partly  overcast  the  haze  will  not 
be  so  pronounced  as  on  a  clear  day.  At  times,  when 
the  sky  is  completely  overcast,  the  haze  will  be  prac- 
tically at  a  minimum.  This  is  on  account  of  the  rays 
that  cause  the  haze  being  absorbed  by  the  clouds. 

Wratten  Screen 

Photographic  plates  and  films  are  more  active  to 
rays  of  blue  and  purple  colors  than  to  yellow,  red,  or 
green  rays.  Therefore  it  is  obvious  that  if  a  plate  or 
film  is  exposed  to  the  ground  from  above  the  bluish 
haze,  the  light  in  the  haze  will  act  on  the  plate  or 

154 


AERIAL    PHOTOGRAPHY 

film  more  rapidly  than  the  rays  actually  coming  from 
the  ground.  This  will  "fog"  the  plate  or  film,  and 
the  exposure  will,  in  nine  cases  out  of  ten,  be  a  failure. 
However,  this  difficulty  has  been  met  and  methods  of 
counteracting  the  haze  and  somewhat  eliminating  the 
bluish- violet  rays  have  been  discovered.  The  best 
method  to  employ  for  this  purpose  is  the  use  of  a 
wratten  screen  or  light  filter.  This  is  an  attachment 
to  be  placed  on  the  lens  of  a  camera  and  is  fitted  with 
a  screen  of  light-yellow  color.  This  attachment  al- 
lows the  red,  yellow,  and  green  light  rays  to  pass 
through  the  lens,  and  stops  the  greater  proportion  of 
the  bluish- violet  rays,  according  to  the  density  of  the 
screen  color.  These  screens  are  manufactured  in 
light,  medium,  heavy  arid  extra  heavy;  for  all  prac- 
tical purposes  the  light  shade  is  recommended  for 
use  in  winter  and  dull  days,  and  the  medium  at  all 
other  times.  A  longer  exposure  is  necessary  with 
these  screens.  With  the  extra-heavy  screen,  ten 
times  the  period  of  normal  exposure  is  required;  the 
reason  for  the  light  and  medium  screens  is  therefore 
obvious. 

These  screens  are  of  great  assistance  on  occasions 
when  fog  or  light  clouds  intervene  between  the  object 
and  the  camera.  The  red,  yellow,  and  green  rays, 
being  of  longer  wave  length  than  the  blue,  violet,  and 
purple  rays,   they  penetrate  the  fog  or  mist  much 

155 


THE    EYES   OF   TJ^E   ARMY   AND    NAVY 

better;  and  therefore  diminish  the  possibiHty  of  the 
plate  or  film  being  foggfed  by  the  bluish-violet  rays. 

In  the  British  Isles  there  are  very  few  days  when 
a  wratten  screen  is  not  beneficial.  For  official  use 
heavy  screens  are  often  used,  as  the  object  is  to  get 
clear  detail  rather  than  true  representation  of  colors. 

Special  plates,  made  relatively  more  sensitive  to 
red,  yellow,  and  green  rays,  are  now  manufactured  and 
used  largely  in  conjunction  with  the  screens  for 
aeronautical  photography. 

Body  of  Camera 

Cameras  of  the  non-collapsible  type  are  recom- 
mended for  aerial  work,  but  on  account  of  lack  of 
room  in  aeroplanes  they  cannot  always  be  carried. 
With  folding  cameras  care  should  be  taken  that  the 
camera  is  correctly  opened  out  and  adjusted.  If  the 
folding  portion  is  of  flexible  material,  the  side  exposed 
to  the  direction  of  the  aeroplane  should  be  protected 
against  the  force  of  the  air;  otherwise  the  rushing 
wind  will  bear  against  the  side  and  may  obscure' part 
of  the  plate  from  the  lens. 

The  Shutter 

The  special  aeronautical  cameras  are  fitted  with 
focal  shutters.     These  have  a  distinct  advantage  over 


AERIAL    PHOTOGRAPHY 

any  other  type,  as  they  permit  more  light  to  pass. 
Shutters  of  this  type  require  deHcate  handHng  and 
offer  great  difficulties  in  repairing.  They  should  be 
carefully  calibrated  and  occasionally  checked. 

The  View-finder 

The  view-finder  should  be  of  the  "direct  view'* 
pattern;  the  wire  grid  type  is  recommended.  The 
finder  should  be  first  adjusted  correctly;  with  a  little 
practice  an  operator  can  locate  the  exact  lines  of 
the  photograph.  The  most  common  fault  is  to  show 
too  little  ground,  and,  although  this  is  an  error  on 
the  right  side,  it  often  causes  needless  waste  of  plates 
when  large  areas  are  being  photographed  to  be 
mounted  together. 

Exposures 

It  is  a  common  belief  that  as  an  aeroplane  is  usually 
traveling  at  a  great  speed  a  very  quick  exposure  is 
required  in  order  to  get  the  best  results;  but  this  is 
not  the  case.  The  higher  a  machine  is  flying  the 
longer  a  plate  or  film  may  be  exposed  with  safety. 
Recent  experiments  have  proved  that  exposures  of 
^z  of  a  second  duration,  taken  at  a  height  of  5,000 
feet  from  a  fast  aeroplane,  were  very  successful.  For 
all  official    aeroplane   photography,   an    exposure   of 

157 


THE  EYES  OF  THE  ARMY  AND  NAVY 

ifV  of  a  second  is  usually  recommended;  and  from  an 
airship  or  balloon  an  exposure  of  ^  of  a  second  is 
required;  but  as  the  atmospheric  conditions  vary 
greatly,  no  exact  table  can  be  laid  down. 

Plate  Slides 

Plate  slides  for  aerial  work  should  be  made  of 
wood,  preferably  teak.  The  much-used  vulcanite 
slides  soon  become  brittle  and  crack  and  are  liable  to 
accumulate  dust,  which,  in  time,  gets  transferred  to 
the  plates  and  spotty  photographs  are  the  result. 
Boxes  holding  from  12  to  18  plates  are  now  used  con- 
siderably, taking  the  place  of  plate  slides.  They  save 
much  time  and  are  more  convenient  to  operate  than 
slides,  although  the  disadvantage  is  that  if  any  mis- 
hap occurs  all  the  plates  may  be  spoiled. 

Actinometer 

An  actinometer  is  a  very  useful  instrument  and 
should  be  included  with  every  aerial  photographer's 
outfit.  This  instrument  is  shaped  like  a  watch  and 
enables  a  person  to  test  the  quality  of  the  light,  with- 
out reference  to  tables  or  to  his  own  sense  of  light 
value.  It  is  also  possible,  by  its  means,  to  ascertain, 
with   some   degree  of   certainty,  before   leaving  the 

J58 


AERIAL    PHOTOGRAPHY 

ground,  whether  successful  photography  can  be  carried 
on ;  it  is  often  of  assistance  in  preHminary  preparations 
such  as  choice  of  shutter,  aperture,  or  shade  of  screen 
Hkely  to  be  required.  When  the  actinometer  is  sup- 
pHed,  full  instructions  of  how  to  use  it  should  be  given 
with  the  instrument. 

Plates  Recommended 

Paget  Orthochromatic,  extra  special  rapid,  specially 
hardened. 

Norris  Isochromatic,  rapid  exposure.  (American 
production.) 

Wellington  extra  speedy. 

Imperial  special  rapid. 

Printing  Papers  Recommended 

Kodak,  Platino  Matto,  rapid,  smooth. 
Wellington  gaslight,  S.  C.  P.  medium,  is  best  for 
very  thin  plates  or  film  exposures. 

Developing 

Time  methods  of  development  give  the  best  and 
quickest  results  and  are  the  only  methods  applicable 
to  orthochromatic  plates.     The  best  developer  to 

159 


THE  EYES  OF  THE  ARMY  AND  NAVY 

use  is  pyrometol.     This  can  be  obtained  in  tabloid 
form,  or  can  be  made  up  in  fresh  solution,  but  the 
former  is  advised. 
To  make  up  the  fresh  solutions: 

A  B 

Metabisulphite  soda  240  grains  Carbonate  soda 8    oz. 

Pyrog.  acid 100     "  Sulphite  soda 2>^  " 

Metol 90     "  Water 40     " 

Potass,  brom 40     " 

Water 40  oz. 

Equal  parts  of  A  and  B. 

If  the  fresh  solutions  are  used,  the  following  points 
should  be  observed:  A  solution  should  not  be  kept 
made  up  for  more  than  a  few  days.  The  two  solu- 
tions mixed  should  not  be  used  after  two  days.  When 
developing  by  the  time  method,  a  pint  of  solution 
will  be  sufficient  to  develop  one  dozen  plates;  it  is 
advisable  to  commence  with  less  than  the  required 
amount  and  add  a  little  fresh  solution  as  each  plate 
is  developed.  The  developing  pans  should  be  heated 
before  the  fluid  is  poured  in  and  should  be  kept  hot 
during  the  process  of  development.  This  can  be 
done  by  placing  the  developing  dish  in  a  pan  of  hot 
water.  The  specially  hardened  plates,-  used  when 
quick  results  are  required,  can  be  safely  developed  in  a 
solution  with  a  temperature  of  about  150°- 2  00° 
Fahrenheit.     The  following  table  indicates  the  time, 

160 


AERIAL    PHOTOGRAPHY 

necessary  to  develop  fully  exposed  negatives  in  order 
to  obtain  the  best  results. 


Temperature  of  developing  solution  in 
degrees  Fahrenheit 


Paget  Orthochromatic  .  .  . 

Norris  Isochromatic 

Imperial  and  Wellington . 


45 
Mins. 


50° 
Mins. 


7 
7 


55° 
Mins. 


4M 

5 

4K 


6o° 

Mins. 


4 

4M 

3H 


65° 

Mins. 

3 

3K 
3K 


70°   I   75° 
Mins.  I  Mins. 

3  2% 

2H^    2% 


In  cases  where  plates  have  been  known  to  be  under- 
exposed it  is  advisable  to  have  the  solution  at  a 
slightly  higher  temperature.  In  cases  of  known 
over-exposure  the  best  results  are  obtained  by  develop- 
ing the  plates  for  one-half  the  time,  then  fix,  and 
intensify  after  washing. 

Fixing  solution  should  be  kept  as  strong,  and  of  the 
same  temperature,  as  the  developing  solution. 


Printing 

The  method  of  printing  aerial  photographs  does 
not  vary  much  from  the  methods  usually  employed 
in  ground  photography,  and  for  all  practical  purposes 
the  same  methods  are  advised. 


XIII 

BOMBS   AND    BOMB-DROPPING 

Types  of  Bombs 

BOMBS  weighing  from  lo  to  25  pounds  are  known 
as  light  bombs.  The  case  is  usually  sheet- 
metal  case  and  is  filled  with  amatol  or  trotyl.  Ob- 
ject: To  drop  a  trail  of  bombs  across  a  building  to 
make  sure  of  a  hit. 

There  are  two  types  of  heavy  bombs,  the  light 
case  (sheet-steel)  and  the  heavy  case  (cast).  Heavy 
bombs  are  also  filled  with  amatol  or  trotyl.  Ob- 
ject: For  submarine  destruction.  If  a  submarine  is 
on  the  surface,  bombs  fitted  with  direct-action  fuse 
should  be  used.  If  submerged,  delay-action  fuse 
would  give  the  best  results.  For  attacking  buildings: 
If  dropped  from  a  height  above  three  thousand 
feet  direct-action  fuse  should  be  used,  and  if  dropped 
from  an  altitude  under  three  thousand  feet  delay- 
action  fuse  would  be  desirable.  For  attacking  earth- 
works: Delay-action  fuse  would  give  the  best  re- 
sults. 

162 


BOMBS    AND    BOMB-DROPPING 

Petrol,  incendiary  and  carcass  bombs  are  filled 
with  petrol  and  secret  composition  and  are  used  for 
the  destruction  of  hostile  materials  and  inflammable 
goods.  Parachute  flares  are  used  to  show  up  enemy- 
positions  by  night  and  for  night-landing  purposes. 
Signal  flares  are  used  for  signaling  purposes  and  may 
be  made  so  as  to  give  a  white  or  colored  light. 

Method  of  Arming  Bombs 

In  a  work  of  this  kind,  descriptions  of  the  various 
methods  of  arming  bombs  would  be  out  of  place  and 
would  also  be  a  contravention  of  the  "Defense  of  the 
Realm  Regulations,"  but  it  may  be  taken  as  practi- 
cally general  that  small  bombs,  bombs  weighing  up 
to  25  pounds,  are  armed  before  they  are  placed  on  the 
bomb-dropping  frame  and  bombs  weighing  more  than 
25  pounds  are  usually  armed  after  being  placed  on 
the  frame. 

Method  of  Carrying  and  Releasing  Bombs 

Bomb-carrying  frames  are  usually  attached  under 
the  lower  planes  and  near  the  fuselage  or  nacelle, 
and  in  some  types  of  machines  under  the  fuselage  to 
the  rear  of  the  undercarriage.  Small  bombs  are 
generally  carried  in  series  of  fours  and  eights  and 
the  larger  bombs  in  couples.  The  releasing  lever  is 
placed,  either  inside  the  fuselage  or  nacelle  or  on  the 

163 


THE  EYES  OF  THE  ARMY  AND  NAVY 

outside  within  easy  reach  of  the  pilot  or  observer, 
and  the  gear  is  arranged  so  as  to  drop  the  projectiles 
alternatively,  first  from  the  one  side  and  then  from 
the  other  side;  this  insures  the  lateral  stability  of 
the  machine  not  being  interfered  with  by  the  weight  of 
the  bombs. 

Bomb-dr6pping 

Best  results  in  bomb-dropping  are  obtained  by 
dropping  head  to  wind,  or,  as  termed  in  the  services, 
"up  wind";  however,  if  conditions  do  not  permit  of 
this  method  a  pilot  should  endeavor  to  drop  his  bombs 
tail  to  wind  or  "down  wind."  Many  types  of  bomb- 
dropping  frames  and  sights  are  used  in  the  service  and 
a  pilot  will  be  instructed  in  their  proper  use.  When 
attacking  an  object  with  a  number  of  small  bombs  the 
best  results  are  obtained  by  "straddling"  the  target; 
that  is,  by  dropping  the  first  bomb  just  previous  to  the 
target  appearing  on  the  bomb  sight  and  dropping  the 
last  bomb  just  after  the  sight  has  passed  over  the 
object.  If  this  method  is  adopted  a  sure  hit  by  one 
or  more  of  the  bombs  is  probable. 

How  to  Ascertain  Direction  of  Wind  when  Flying 

There  are  many  methods  of  ascertaining  the 
direction  of  the  wind  when  ready  to  drop  bombs. 
Smoke  drift  from  factory  chimneys  or  dwellings  is 
an    excellent    guide.      Bomb-dropping    over    enemy 

164 


BOMBS    AND    BOMB-DROPPING 

country  is  generally  carried  out  from  a  height  of  be- 
tween 10,000  and  15,000  feet,  however;  unless  the 
visibility  is  very  good  these  smoke  signs  would  be 
very  indistinct.  The  best  method  to  adopt  under  such 
conditions  is  to  ascertain  the  drift  of  the  machine. 
When  preparing  to  drop  bombs  the  pilot  should  head 
his  machine  in  the  direction  from  which  he  assumes 
the  wind  to  be  blowing,  and  then  take  a  line  of 
two  objects  ahead,  along  the  side  of  the  fuselage  or 
nacelle.  Suppose  he  chooses  a  village  far  ahead,  and 
a  forest  is  between  the  village  and  the  machine,  on  the 
left  or  port  side  of  the  machine.  He  should  endeavor 
to  steer  straight  along  the  line  of  the  two  objects.  If, 
however,  the  forest  disappears  under  the  fuselage  or 
nacelle,  he  knows  that  he  is  drifting  to  port,  or  to 
the  left  of  the  machine;  therefore  the  wind  is  slightly 
to  his  right.  If  in  the  other  case  the  forest  appears  to 
be  moving  toward  the  port  wing-tip,  the  machine 
is  drifting  to  his  right,  or  starboard,  and  indicates 
that  the  direction  of  the  wind  is  slightly  to  his  left. 
By  carrying  out  this  procedure  a  few  times  the  true 
direction  of  the  wind  can  be  ascertained 

The  Theory  of  Bomb-dropping. 

A  bomb  has  two  forces  to  resist.     The  force  of 
gravity  and  the  force  of  forward  velocity.    The  differ - 
12  165 


THE  EYES  OF  THE  ARMY  AND  NAVY 


ence  between  the  time  of  the  fall  of  a  bomb  in  vacuum 
and  the  fall  of  a  bomb  under  ordinary  conditions  is 
termed  the  "time  lag,"  and  the  difference  of  the 
distance  traveled  forward  on  the  ground  between  the 
two  is  termed  the  "ground  lag."     (Fig.  41.) 

An  endeavor  has  been  made  to  dispense  with  all 
formulae  in  this  work,  but  there  are  two  simple  for- 


Line  A  indicates  trajec- 
tory of  bomb  dropped  in 
a  vacuum. 

B — trajectory  of  bomb 
dropped  under  normal  con- 
ditions. 

CD — time  lag. 

HF — ground  lag. 

E — position  of  machine 
when  bomb  is  dropped. 

R — ^position  of  machine 
when  bomb  in  vacuum 
strikes  the  ground. 


mulae  in  the  theory  of  bomb-dropping  which  every 
pilot  should  master;  these  can  be  easily  worked  out  if 
the  application  of  "square  root"  is  understood.  At 
the  end  of  this  chapter  a  few  lines,  explaining  how  to 
ascertain  the  square  root  of  a  number  and  how  to 
apply  it,  are  given. 

166 


BOMBS    AND    BOMB-DROPPING 

To  ascertain  the  time  of  fall  of  a  bomb,  if  given  the 
height  at  which  it  is  dropped: 

H  H  ,^.         .... 

—   + =  Time  of  fall  - 

4  9000 

.  /  Height  in  feet  Height    /  H     .      .       ,     \ 

V +  I IS  time  lag  I 

^  4  9000      \9000  / 

Example:  Machine  is  flying  at  6,400  feet;  therefore 
the  time  of  fall  is 

.  /  6400  6400 

^       4  9000 

The  square  root  of  6,400  is  80,  therefore: 

+  - — —    =  20.7  seconds  (approximately) 

4  9000 

To  ascertain  the  distance  a  bomb  travels  forward 
from  a  point  on  the  ground  vertically  beneath  the 
machine,  at  the  time  of  release,  to  a  point  where  the 
bomb  strikes  the  ground: 

/  /  H  .  H  \  Speed  of  machine  H      ,  1 ,    \  I 

(V + )   X    .    ,    ,  , (groundlag) 

N      4  9000/  m  feet  per  second  40  J 

Example:  Machine  is  at  8, 100  feet,  speed  of  machine 
is  100  feet  per  second.  Find  distance  bomb  travels 
forward,  from  the  moment  of  release  to  the  time  of 
striking  the  ground: 

167 


THE  EYES  OF  THE  ARMY  AND  NAVY 

The  square  root  of  8,ioo  is  90,  therefore: 

90  8100  8100  o    ,  /  .  ,       N 

+  X   100  —     ■  =  2138  feet  (approximately) 

4  9000  40 

It  should  be  borne  in  mind  that  in  the  majority  of 
problems  of  this  nature  the  speed  is  either  given  in 
feet  per  second  or  knots  per  hour.  If  the  latter  is 
given,  to  brings  knots  per  hour  to  feet  per  second : 

Multiply  the  number  of  knots  per  hour  by  i .  69 .  This 
will  give  the  approximate  number  of  feet  per  second, 
and  will  be  sufficient  for  all  problems  of  this  nature. 

Square  Root 

If  a  number  be  multiplied  by  itself,  the  product  is 
called  the  square,  or  second  power,  of  the  number. 
Thus  the  square  of  8  is  8X8,  which  is  64.  The 
square  of  a  number  is  symbolized  by  placing  a  small 
figure  at  the  right  of  the  upper  part  of  the  number; 
for  example,  in  the  above,  the  square  of  8  is  8X8, 
and  is  represented  by  8^. 

The  square  root  of  a  given  mmiber  is  that  number 
which  multiplied  by  itself  will  produce  the  given 
number.  For  example,  the  square  root  of  64  is  8 
because  8  times  8  is  64.  The  square  root  of  a  number 
is  denoted  by  the  sign  V    placed  before  the  number; 

thus,  the  square  root  of  64  is  denoted  byV  64. 

168 


BOMBS    AND    BOMB-DROPPING 

Since  V  loo  =  lo,  and  V  10,000  =  100,  and  v  1,000,000 
=  1,000,  it  follows  that  the  square  root  of  any  number 
between  100  and  10,000  lies  between  10  and  100,  and 
consists  of  two  digits;  that  the  square  root  of  any 
number  between  10,000  and  1,000,000  lies  between  100 
and  10,000,  and  consists  of  three  digits,  and  so  on. 
Hence  it  will  be  observed  that  for  two  additional 
digits  of  a  number  in  periods  of  two,  beginning  at  the 
right  hand,  the  number  of  these  periods  will  be  the 
same  as  the  number  of  digits  in  the  square  root.  The 
left-hand  period  will  sometimes  contain  only  one 
digit.  Consider  the  number  1,444,  obtained  by  multi- 
plying 38  by  38.    Its  square  root  is  38, 

In  ascertaining  this  square  root  first  determine  the 
number  of  tens,  and  then  the  number  of  units. 

Write  38  in  the  form  30  -|- 8,  and  multiply  it  by  30  -f  8, 
thus,    • 

30+8 

30+8 

30x8+32 
30H        30X8 

30^+2  X30  X8+82 
=  1444  =  3o2  +  (2  X  30  +  8)  X  8. 

The  number  of  tens  in  the  square  root  can  be  found 
by  ascertaining  what  multiple  of  10  has  its  square 
next  less  than  1,444;  this  is  clearly  30,  for  40^  =  1,600 
and  is  too  great. 

169 


THE  EYES  OF  THE  ARMY  AND  NAVY 

Having  found  the  tens,  next  find  the  units. 

Subtracting  30^,  or  900,  from  1,444,  the  remainder 
is  544;   hence  544  must  be  equal  to  (2  X30+8)  X8. 

If  544  could  be  divided  by  2  X30+8  the  number  of 
units  8  would  be  obtained.  But  since  the  divisor 
itself  involves  this  unascertained  number  8,  the 
plan  adopted  is  to  use  the  part  2  X30  as  a  trial  di- 
visor, to  find  by  means  of  it  a  trial  quotient,  and  then 
to  see  whether  (2X3o+trial  quotient)  X trial  quo- 
tient =544. 

The  first  trial  quotient  may  not  prove  correct;  if 
it  proves  to  be  too  great,  try  the  number  next  less, 
and  so  on. 

In  this  particular  case,  divide  544  by  2  X  30, 
i.e.,  by  60,  and  the  trial  quotient  9  is  obtained.  But 
(60-I-9)  X9  =621,  and  is  too  great;  therefore  try  8, 
and  (6o-i-8)  X8  =  544  is  the  result. 

The  digits  of  the  square  root  38  are  thus  found  in 
succession. 

The  above  operations  may  be  stated  concisely  thus : 


i4;44|30+  8,  or  thus, 

900 


14/441 38 
9 


60-1-8 


544  68 

544 


544 
544 


In  the  latter  form,  which  is  the  practical  one,  the 
process  is  briefly  stated  as  follows: 

170 


BOMBS   AND    BOMB-DROPPING 

Mark  off  the  digits  in  twos,  beginning  at  the  right  hand. 

The  greatest  square  in  14  is  9,  and  its  square  root  is  3.  Place 
3  in  the  root  place.  Multiply  3  by  3,  and  subtract  the  product 
from  14.     The  remainder  is  5. 

To  this  remainder  annex  the  period  44,  and  the  dividend  be- 
comes 544.     Twice  the  root  digit  3  is  6,  so  put  6  in  the  divisor. 

Instead  of  60  take  6  as  a  trial  divisor,  and  take  54  as  a  trial 
dividend.  Proceeding  as  explained  above,  it  will  be  readily 
observed  that  8  is  the  true  quotient.  Annex  8  to  the  3  in  the  root 
place,  and  also  to  the  divisor.  Multiply  68  by  8,  and,  subtracting 
the  product  from  544,  there  will  be  no  remainder,  and  the  operation 
is  completed. 

The  square  root  is  thus  38. 

In  this  way  a  square  root  can  be  obtained,  however 
many  digits  the  number  may  have. 

Example:    Find  the  square  root  of  56,644. 


ist.  Mark  off  the  digits  in  periods  of  two,  beginning  at 
the  right  hand. 

2d.  The  root  nearest  to  that  of  the  first  period  5     2 
is  2.    The  square  of  2  is  4.     Subtracting  4  from  5, 
the  remainder  is  i.     Bringing  down  the  second  43 
period,  166  is  the  next  dividend. 

3d.  The  trial  divisor  is  2  X  2,  or  4,  and  the  trial     gg 
dividend  is  16.     The  true  quotient  is  3.     Place  3 
as  the  second  digit  in  the  root,  and  also  annex  3  to 
the  trial  divisor. 

4th.  The  next  trial  divisor   is  46,  obtained  by  doubling  the 
23  in  the  root;  and  the  trial  dividend  is  374. 


5,66,44  1 238 

4 

166 

129 


3744 
3744 


XIV 

NIGHT    FLYING 

NIGHT  flying  is  a  comparatively  new  and  special 
branch  of  the  aerial  services,  and  duties  in  this 
connection  are  usually  carried  out  by  bombing  squad- 
rons and  by  defensive  squadrons  engaged  in  inter- 
cepting hostile  aircraft.  A  pilot  recommended  for 
such  duties  receives  special  instruction  and  is  practi- 
cally obliged  to  fly  by  means  of  the  instruments.  The 
preliminary  instruction  consists  of  flying  during  the 
evening  and  staying  up  later  every  night  until  pro- 
ficient. 

In  "taking  off"  and  landing  it  is  imperative  that 
a  pilot  should  get  head  to  wind  and  maintain  perfect 
lateral  stability.  Machines  for  night  flying  are 
usually  equipped  with  wing-tip  and  tail  lights  and 
the  instruments  have  illuminated  ciphers  as  well  as  a 
pilot  light  in  the  cockpit.  In  "taking  off"  and  pre- 
paring for  formation  flying  the  wing-tip  and  tail 
lights  are  used,  but  on  approaching  enemy  territory 

172 


NIGHT    FLYING 

they  are  extinguished  and  are  not  used  again  until 
over  friendly  country. 

Landing  at  Night 

Landing  at  night  is  most  difficult,  especially  in  a 
small  aerodrome.  Each  aerodrome  should  have  pre- 
arranged signals  so  that  a  pilot  passing  over  an  air 
station  would  know  whether  he  had  arrived  at  his 
own  station.  For  instance,  a  pilot  from  X  station 
would  fire  a  prearranged  colored  light  when  over  an 
air  station,  and  if  the  correct  prearranged  colored 
signal  was  fired  from  the  ground  in  answer  he  would 
know  that  he  had  arrived  at  his  own  aerodrome;  but 
if  a  different  colored  light  was  fired,  it  would  signify 
that  he  was  at  an  air  station  other  than  where  he  was 
stationed.  When  a  pilot  is  ready  to  land  he  gives 
the  landing  signal  and  the  landing  flares  or  search- 
lights are  lit. 

Methods  of  Placing  Landing  Flares 

There  are  many  methods  of  placing  landing  flares; 
the  most  commonly  adopted  is  to  place  a  number  of 
flares  in  the  field  so  as  to  form  the  letter  L  in  ac- 
cordance with  the  direction  of  the  wind.     (Fig.  42.) 

A  pilot  landing  would  be  required  to  touch  the 
ground  at  the  end  of  the  long  arm  of  the  L  and  land 
in  the  direction  of  the  short  arm  of  the  L. 

173 


THE  EYES  OF  THE  ARMY  AND  NAVY 

All  other  lights  within  a  radius  of  one  mile  of  the 
landing-ground  should  be  extinguished  and  parts  of 

O O O O — 9 

rig.  42  I 


Direction   in   which  a, 
pilot  should  land 


I 

6 


the  landing-ground  likely  to  cause  damage  should  be 
marked  with  red  lights. 

On  a  bright  moonlight  night  flares  and  searchlights 
may  be  dispensed  with  and  the  same  signal  used  as 
for  day  flying. 

It  is  a  common  practice  to  fire  rockets  or  signal 
lights  from  the  aerodrome  to  attract  an  aeroplane 
when  in  the  vicinity. 

Parachute  flares  are  usually  carried  on  machines  on 
night-flying  duties,  and  these  flares  are  useful  on  oc- 
casions when  a  pilot  has  a  forced  landing.  It  consists 
of  a  flare  attached  to  a  parachute  and  is  launched 
from  an  electric  launching  tube.  It  burns  for  a  short 
period  and  gives  a  pilot  an  idea  of  the  country  he  is 
over.  When  this  parachute  has  been  fired  it  is 
necessary  for  the  pilot  to  pilot  his  machine  between 
the  flare  and  the  ground,  otherwise  his  vision  of  the 
ground  would  be  obliterated  by  the  glare. 

174 


XV 

ARTILLERY   OBSERVATIONS   FROM   AIRCRAFT 

Shells  Used  by  the  Artillery 

THE  following  notes  on  "spotting"  are  given  as  a 
guide  to  pilots  and  observers  working  with  the 
artillery. 

The  shell  used  by  the  artillery  consists  of  shrapnel, 
high  explosive,  and  common  shell. 

Shrapnel  may  burst  either  with  a  time  or  percussion 
fuse.  When  a  time  fuse  is  used  effective  shell  should 
burst  above  the  ground  and  from  twenty-five  to 
seventy-five  yards  short  of  the  target;  the  bullets 
from  the  shell  then  carry  on  into  the  target. 

Shrapnel  has  a  great  effect  on  personnel,  but  very 
little  effect  on  material.  When  shrapnel  shells  burst 
in  the  air  they  are  easy  to  see,  but  difficult  to  observe 
when  they  burst  on  striking  the  ground. 

High-explosive  shells  are  sometimes  very  difficult 
to  see  when  they  detonate,  particularly  on  striking 
soft  ground.  Shells  of  the  high-explosive  type  that 
detonate  produce  a  black  smoke,  and  shells  that  do 

175 


THE  EYES  OF  THE  ARMY  AND  NAVY 

not  detonate  produce  a  whitish-green  smoke.  High- 
explosive  .  shells  have  great  material  but  extremely- 
local  effect;  a  burst  about  five  yards  from  a  trench 
may  do  Httle  or  no  damage. 

Signaling  from  an  Aeroplane 

When  a  battery  is  "ranging"  one  gun  only  is 
generally  used. 

There  are  three  methods  of  signaling  from  an 
aeroplane  to  the  ground:  wireless,  lamps,  and  signal 
lights;  but  for  artillery  work  the  wireless  is  the  most 
common. 

Before  going  up  an  observer  should  find  out  ex- 
actly what  is  required.  The  fire  may  be  for  effect, 
or  merely  to  register  certain  definite  points.  Again,  a 
battery  commander  may  want  to  correct  the  line  and 
range  of  all  the  guns  of  his  battery  and  so  require  ob- 
servation of  fire  for  each  one,  or  may  only  want 
observation  for  the  particular  one  selected  to  carry  out 
the  ranging. 

Location  of  Targets  and  Ranging 

The  direction  and  range  are  taken  from  a  square  of 
the  map  as  reported  by  the  observer,  who  then 
proceeds  to  correct  the  fire  by  the  usual  methods. 

176 


O  P 

^^  H! 

cro  CO 

^  r  p 

^  •  "^ 

«2  3. 


ARTILLERY    OBSERVATIONS 

When  signal  lights  or  smoke  puffs  as  signals  are 
used  the  position  of  the  target  can  be  shown  by  the 
aeroplane  flying  to  a  position  vertically  over  the 
target  and  then  giving  a  signal.  The  range  may  be 
obtained  by  the  angle  of  sight  of  the  aeroplane.  When 
this  method  is  adopted  the  aeroplane  flies  at  a  pre- 
arranged height  and  the  angle  of  sight  is  taken  at  the 
moment  when  the  aeroplane  signals  that  it  is  verti- 
cally over  the  target. 

When  "spotting"  with  machines  equipped  with 
wireless,  prearranged  symbols  are  used.  The  station 
or  stations  answer  the  signals,  either  by  lamp  or  by 
placing  strips  of  linen  on  the  ground.  When  the 
battery  is  ready  to  fire  the  ground  station  puts  out  a 
signal,  and  the  observer  acknowledges  it  and  then 
sends  a  symbol  for  "stand  by,"  followed  by  the 
symbol  for  the  target  for  which  he  is  going  to  "range." 
He  then  flies  to  a  convenient  position  for  observing 
the  fall  of  shell  and,  when  ready,  gives  the  signal  to 
open  fire.  The  battery  repeats  each  signal  sent  by 
the  observer  and  the  aeroplane  sends  a  general 
answer  in  acknowledgment.  This  practice  eliminates 
the  likelihood  of  any  mistakes.  When  the  com- 
mander of  the  battery  decides  that  he  has  obtained 
sufficient  results  he  gives  the  signal  for  the  observer 
to  range  for  the  next  target. 

When  an  observer  desires  to  give  the  commander 

177 


THE  EYES  OF  THE  ARMY  AND  NAVY 

of  a  battery  more  information  than  can  be  conveyed 
by  signals  it  is  necessary  for  him  to  fly  over  the 
station  and  drop  a  message  bag.  There  are  many 
methods  of  giving  range  adopted,  but  for  reasons  that 
must  be  obvious  they  cannot  be  disclosed  in  this 
work. 

Ranging 

When  a  round  is  fired  the  observer  notes  it  fall  with 
reference  to  imaginary  squares  or  circles  on  the 
ground,  the  target  being  calculated  as  the  middle 
square  or  center  of  the  circle.  These  squares  or 
circles  are  numbered,  and  by  signaling  the  number 
or  symbol  of  the  square  or  circle  where  the  shell  falls 
the  battery  commander  can  refer  to  the  adopted 
method  and  make  corrections. 

This  procedure  is  carried  on  until  the  shells  hit  the 
target,  then  the  "battery  fire"  signal  is  given  and 
firing  is  carried  on  until  the  "cease  firing"  order. 

Observers  should  always,  when  possible,  watch  the 
battery  to  see  if  the  gun  fires  when  the  signal  is  given, 
as  then  there  is  less  chance  of  the  burst  being  missed  if 
it  is  reasonably  near  the  target.  It  is  not  a  good  prac- 
tice to  stare  at  the  target;  the  observer  should  watch 
as  wide  an  area  as  possible  which  has  the  target  for 
its  center,  otherwise  a  burst  far  from  the  target  will 
almost  certainly  be  missed.     When  an  actual  battle 

178 


ARTILLERY   OBSERVATIONS 

is  in  progress  the  number  of  targets  will  be  large, 
and  in  order  to  produce  the  best  results  both  pilot  and 
observer  should  do  the  maximum  amount  of  work 
possible.  If  the  observer  does  the  ranging,  the  pilot 
should,  to  a  certain  extent,  watch  him  to  see  where 
he  wishes  to  go,  when  endeavoring  to  locate  new 
targets;  therefore,  pilots  as  well  as  observers  should 
receive  training  in  observation  of  artillery  fire. 

Hints  for  Artillery  Observers 

(i)  Do  not  send  wireless  messages  while  the  ma- 
chine is  turning,  and  avoid  sending  when  directly  over 
ground  stations. 

(2)  If  the  ground  station  is  experiencing  difficulty 
in  receiving  your  signals,  send  only  when  flying 
toward  it  from  the  target.  This  may  be  foimd 
laborious,  but  will  often  save  a  shot  from  being  an 
entire  failure. 

(3)  Before  commencing  work  with  a  ground  station 
always  give  the  operator  a  chance  of  tuning  his 
instrument  into  you.  It  is  impossible  to  do  this  when 
you  are  very  low  and  near  the  ground  station.  Fly 
toward  the  station,  calling  it;  when  over  it  turn  and 
fly  away,  and  commence  to  call  again  when  not 
directly  over  it. 

(4)  Limit  your  signals  to  as  few  as  possible. 

179 


THE  EYES  OF  THE  ARMY  AND  NAVY 

(5)  Send  your  Morse  characters  with  precision. 

(6)  Do  not  send  too  quickly,  but  avoid  wasting 
time  between  signals. 

(7)  During  the  first  few  rounds  on  a  new  target 
allow  time  to  elapse  between  the  observation  and  the 
next  "Go  ahead"  signal,  especially  if  the  battery 
has  started  rather  wide  of  the  mark.  From  two  to 
two  and  a  half  minutes  should  be  ample  for  any 
battery. 

(8)  Slow  shots  are  often  due  to  slow  observing.  In 
order  to  observe  quickly  it  is  necessary  to  manoeuver 
for  a  good  position. 

(9)  In  a  shot  for  effect  inform  the  battery  when  to 
change — that  is,  when  the  first  target  is  sufficiently 
dealt  with. 

(10)  When  you  see  that  another  battery  than  the 
one  you  are  assisting  is  dropping  shells  near  your 
target,  make  up  your  mind  at  once  if  you  are  going 
to  be  able  to  range  your  battery  on  it  or  not.  If  you 
decide  that  it  is  impossible,  change  to  another  target. 


XVI 

AERIAL   FIGHTING 

ALL  pilot-students  hope  to  become  "star"  aviators. 
l\  In  reality,  only  those  possessing  very  special  qual- 
ities ever  succeed  in  attaining  such  extraordinary 
superiority. 

The  "star"  pilot  must  be  fearless  and  at  the  same 
time  cautious.  He  must  first  of  all  possess  "flying 
sense"  that  enables  him  to  throw  his  machine  about 
in  apparent  abandon,  while,  in  fact,  it  is  at  all  times 
under  perfect  control.  To  acquire  this  proficiency 
the  pilot  must  have  experimented  extensively  with 
all  the  tricks  and  "stunts"  in  the  aeronautical  cate- 
gory, including  looping,  tail  sliding,  and  tail  spinning, 
side  slipping,  rolling,  and  nose  diving.  These  evolu- 
tions must  be  practised  in  a  suitable  machine  and 
never  at  a  lower  elevation  than  5,000  feet.  The  limit 
of  your  machine's  capacity  in  structural  strain  must 
be  always  kept  in  mind. 

A  cool  head  and  quick  wits  are  essential  to  the 
13  181 


THE  EYES  OF  THE  ARMY  AND  NAVY 

successful  air  fighter.  You  have  successful  fighters 
among  your  enemies;   they  must  be  surpassed. 

One  must  have  perfect  eyesight;  above  all,  one 
must  keep  himself  at  all  times  absolutely  fit,  phys- 
ically. 

Following  are  a  few  suggestions  regarding  the  or- 
dinary day's  work  of  the  fighting  pilot: 

Formation  Flying 

Type  of  machine  considered,  Sopwith  Scout.  Num- 
ber of  machines,  five.     130-H.P.  Clerget  motor. 

On  leaving  the  ground  the  flight  leader  must  choose 
suitable  pilots  to  fly  together,  and  having  chosen  them 
must  let  them  always  fly  together  and  in  the  same 
positions  in  the  formation  as  far  as  possible.  He 
must  endeavor  never  to  let  the  pilot  fly  any  machine 
but  his  own  over  the  lines. 

He  is  responsible  for  his  flight  leaving  the  ground 
punctually,  and  to  make  certain  of  this  must  insure 
that  all  pilots  are  dressed  and  comfortably  settled 
in  their  machines  five  minutes  before  the  flight  is  due 
to  start. 

AU  engines,  having  previously  been  tested  by  the 
mechanic  in  charge,  must  be  seen  to  be  running 
"throttled  down."  Then,  on  a  signal  from  the 
ground  officer  that  all  engines  are  satisfactory,  the 
flight  leader  leaves  the  ground.    The  remaining  four 


AERIAL    FIGHTING 

machines,  if  head  to  wind,  should  be  off  the  ground  in 
thirty  seconds,  the  order  of  getting  away  correspond- 
ing to  each  machine's  position  in  the  formation  thus: 

I 

4  5 

The  leader  must  fly  full  out  to  about  700  feet  and# 
in  an  absolutely  straight  direction.  He  then  "throttles 
down  and  flies  his  machine  as  slowly  as  possible," 
meantime  watching  his  pilots  pick  up  formation 
(this  should  not  take  more  than  one  or  two  minutes) . 
This  done,  he  gives  the  "attention"  signal  by  rocking 
his  machine  laterally,  or  by  firing  a  red  Very's  light; 
he  turns  and  heads  to  the  lines  and  opens  up  his  en- 
gine when  the  turn  is  absolutely  completed.  The 
squadron  then  begins  to  climb  and  the  leader  must 
adjust  his  engine  to  the  worst  climbing  machine  as 
quickly  as  possible,  and  having  done  that  thereafter 
alter  his  throttle,  speed,  and  direction  as  little  as 
possible.  He  must  look  round  at  his  formation  at 
least  every  minute.  Do  not  use  a  diamond  forma- 
tion, as  this  leaves  three  rear  machines  open  to  attack 
instead  of  two. 

The  Flying  Officer 

It  is  of  paramount   importance  for  a  flying  officer 
to  be  able  to  use  his  throttle  to  the  full  and  to  be  able 

183 


THE  EYES  OF  THE  ARMY  AND  NAVY 

to  alter  the  angle  of  climb  of  his  machine.  This 
sounds  extraordinarily  easy,  but  it  is  the  root  of  all 
bad  formation. 

Having  left  the  ground,  each  pilot  picks  up  his 
allotted  station  in  order;  i.  e.,  as  close  as  possible  and 
slightly  above  his  next  ahead.  When  flying  in  "V" 
^formation,  pilots  should  fly  as  close  as  possible  to- 
gether, and  the  angle  subtended  by  the  formation 
must  not  be  too  acute;  otherwise  the  leader  will 
have  difficulty  in  watching  his  flight. 

There  is  no  excuse  for  a  pilot  being  astern  of  station 
if  he  is  above  his  next  ahead;  he  must  put  the  nose 
of  the  machine  down  and  catch  up.  Having  once 
picked  up  formation,  it  leads  to  endless  trouble  if  a 
flying  officer  loses  position  and  starts  doing  independ- 
ent circles  of  his  own.  The  slightest  mistake  in  posi- 
tion must  be  instantly  corrected;  do  not  wait  till  the 
error  is  a  big  one.  An  exact  parallel  is  found  in  steer- 
ing a  boat  or  a  car.  A  good  helmsman  keeps  on  his 
course  by  employing  none  but  the  smallest  motions 
of  the  tiller. 

The  evolution  of  altering  course  is  more  difficult. 
The  flight  leader  should  always  turn  in  the  same  direc- 
tion (assume  this  to  be  the  left),  thus  giving  each 
pilot  a  chance  to  learn  his  own  particular  turn. 

The  flight  leader  rocks  his  machine  repeatedly,  and 
pauses;    then  he  does  a  minute  turn  to   the  left,  at 


AERIAL    FIGHTING 

the  same  time  throttling  down  and  putting  the  nose 
of  his  machine  down  a  Httle.  The  two  pilots  on  his 
left  do  a  slight  right-hand  turn,  throttling  down  a 
little  more.  The  two  pilots  on  his  right  commence 
a  left-hand  turn,  keeping  their  engines  full  on.  Then 
the  pilots  on  his  left  both  steer  a  left-hand  turn,  the 
leader  turns  to  the  left,  and  the  two  right-hand  pilots 
carry  on  with  their  left-hand  turn.  Then  the  leader 
straightens  out  and  the  formation  picks  up  its  dress- 
ing, and  the  leader  opens  his  engine  and  carries  on 
as  before.  This  is  the  most  successful  method  of 
turning  a  formation. 

No  further  manoeuver  should  present  great  difficulty 
on  this  side  of  the  hnes. 

Pilots  must  remember  to  fire  their  guns  as  con- 
tinuously as  possible  to  prevent  freezing,  keeping  in 
mind  the  bullet's  ultimate  destination.  Also  remem- 
ber to  look  behind  and  toward  your  formation,  thus 
helping  to  prevent  a  surprise  attack  on  the  other 
"arms"  of  the  formation. 

Crossing  Enemy  Lines 

In  enemy  territory  hostile  aircraft  and  anti-aircraft 
fire  make  an  accurate  formation  a  matter  of  some 
difficulty;  in  practice,  machines  fly  more  in  a  group 
than  in  a  formation.    But  the  more  accurate  the  for- 

185 


THE  EYES  OF  THE  ARMY  AND  NAVY 

mation  the  easier  is  the  task  for  the  already  over- 
worked leader.  The  leader  has  to  keep  his  formation 
together,  to  decide  when  to  attack  hostile  aircraft,  to 
watch  for  hostile  aircraft  about  to  attack,  to  see  that 
his  formation  does  not  lose  its  way,  and  to  attend 
to  many  other  small  points. 

The  flying  officer's  main  duty  is  to  keep  formation 
and  watch  out  for  attacks,  especially  on  the  two  rear 
pilots. 

Signals  Between  Machines 

These  are  in  practice  mostly  given  by  the  leader. 

Rocking  the  machine  laterally  to  attract  attention. 
If  accompanied  by  waving  the  arm,  it  calls  attention 
to  hostile  aircraft  in  whichever  direction  the  arm  is 
waved.  If  followed  by  rocking  the  machine  in  a 
fore-and-aft  direction,  it  means  a  gun  jam. 

Never  wave  except  to  indicate  hostile  aircraft. 

If  a  pilot  wishes  to  communicate  with  the  leader  he 
must  get  in  front  of  him  and  give  the  signal ;  if  unable 
to  do  this,  he  must  communicate  somehow  with  an- 
other pilot,  and  he  will  warn  the  leader.  The  leader 
must  on  no  account  allow  a  returning  pilot  to  cross  the 
lines  unescorted. 

A  green  Hght  means  an  escort  to  the  Hnes  for  engine 
failure  or  any  other  reason. 

If  a  machine  gets  out  of  touch  with  the  formation 

i86 


AERIAL    FIGHTING 

the  squadron  should  go  to  a  previously  arranged  spot 
for  reforming. 

Attacking  Hostile  Aircraft 

The  following  "ten  commandments"  in  aerial  fight- 
ing are  considered  of  vital  importance.  They  may 
appear  cowardly,  but  they  are  compiled  from  the 
experiences  of  the  pilots  that  I  have  come  into  contact 
with  on  active  service. 

(i)  Do  not  lose  formation. 

(2)  Do  not  press  an  attack  on  a  two-seater  that 
fires  at  you  before  you  are  in  perfect  position.  Break 
away  and  attack  it  or  another  hostile  aircraft  later 
with  a  chance  of  surprise. 

(3)  Do  not  stay  to  manoeuver  with  a  two-seater. 

(4)  Do  not  dive  to  break  off  a  combat  unless  you 
are  confident  that  your  machine  is  a  better  "diver" 
than  that  of  the  enemy. 

(5)  Do  not  unnecessarily  attack  a  superior  forma- 
tion; you  will  get  a  better  chance  if  you  wait  five 
minutes. 

(6)  Do  not  attack  without  looking  for  the  machine 
above  you ;  he  will  almost  certainly  come  on  your  tail 
unawares  while  you  are  attacking  if  you  are  not 
watching  him.  Look  behind  continually  while  on  a 
dive, 

187 


THE  EYES  OF  THE  ARMY  AND  NAVY 

(7)  Do  not  come  down  too  low  on  the  other  side  or 
you  will  have  all  the  enemy  on  to  you. 

(8)  Do  not  go  to  sleep  in  the  air  for  one  instant  of 
your  patrol.    Watch  your  tail. 

(9)  Do  not  deHver  a  surprise  attack  at  over  90 
knots  unless  you  wish  to  scare  hostile  aircraft  off 
friendly  machines'  tails.  Most  machines  are  not  easily 
enough  controlled  at  that  speed,  and  the  firing  period 
passes  too  rapidly.  ' 

(10)  Do  not  deliver  a  surprise  attack  at  over  100 
yards'  range  at  the  very  most. 

These  rules  only  apply  to  an  offensive  patrol.  If 
the  hostile  machines  must  be  moved,  they  must  be 
moved  at  all  costs. 

Delivering  an  Attack 

In  delivering  an  attack  remember  that  your  most 
important  asset  is  surprise.  The  commonest  way  to 
effect  this  is  to  wait  till  the  enemy  machine  is  going 
away  from  the  sun ;  then  come  in  on  his  tail ;  also  you 
may  attack  while  he  is  obviously  otherwise  engaged. 
Thus  it  is  often  not  wise  to  attack  immediately.  Some- 
times it  pays  to  find  out  what  is  the  object  of  the 
enemy's  flight  and  attack  him  while  carrying  out  this 
object  and  least  likely  to  be  on  the  lookout  (as  in  the 
case  of  photography). 

i88 


AERIAL    FIGHTING 

While  he  is  attacking  or  waiting  to  attack  a  machine 
an  enemy  presents  little  or  no  defensive. 

When  shadowing  hostile  aircraft  keep  as  far  away 
as  possible  and  keep  to  sunward  of  him. 

Do  not  forget  that  a  single  enemy  machine  at 
low  altitude  is  probably  a  bait,  and  a  counter-attack 
must  be  expected  and  anticipated. 

With  regard  to  the  method  of  attack,  it  is  usually 
best  and  easiest  to  attack  from  behind.  A  right- 
angle  attack  through  the  wing  is  not  usually  success- 
ful. 

Attacking  from  in  front  is  not  to  be  recommended. 
In  practice  the  method  of  attacking  from  behind  is 
the  one  most  used.  But  it  is  very  easy  to  make  a 
failure  of  an  easy  chance. 

Try  and  discover  if  you  have  the  speed  of  the 
hostile  aircraft  flying  level  (always  assuming  you  are 
above  him).  If  you  have  not,  glide  straight  down  to 
him  and  attack  him  on  the  steep  glide,  withholding 
fire  until  within  a  hundred  yards  of  him.  If  you 
have,  dive  well  behind  him  and  come  up  to  him,  very 
slightly  lower,  on  the  throttle.  If  the  attack  is  a  sur- 
prise, place  yourself  about  twenty -five  yards  behind 
him,  very  slightly  below,  and  throttle  down  to  his 
exact  speed,  then  fire.  Have  one  hand  on  the 
throttle  the  whole  time,  and  of  course  the  lanyard 
on  the  trigger  should  always  be  on  the  control  level. 

189 


THE  EYES  OF  THE  ARMY  AND  NAVY 

It  is  very  easy  to  lose  speed  too  far  astern  and  be  so 
long  in  catching  up  that  you  are  observed,  or  to  have 
too  much  speed  and  shoot  by  the  enemy  machine  be- 
fore firing.  The  most  difficult  test  is  to  withhold  fire 
till  the  correct  moment. 

Pilots  learn  their  own  methods  of  attack  from  ex- 
perience; the  following  will  be  found  a  good  one  to 
try,  especially  in  a  Sopwith  Scout.  If,  before  you 
are  in  a  position  to  fire,  you  see  the  observer  produce 
his  gun,  make  off  at  once.  Do  not  stay  to  manoeuver 
with  a  two-seater.  A  scout  is  designed  for  offensive  and 
has  absolutely  no  defensive  except  its  ability  to  escape. 

When  the  leader  attacks  it  is  usual  for  Nos.  2  and 
3  to  accompany  him  down.  No.  2  is  supposed  to 
attack  the  same  machine  as  the  leader,  but  in  practice 
things  arrange  themselves.  If  two  machines  attack 
an  enemy  simultaneously,  it  more  than  doubles  the 
chance  of  success.  Nos.  4  and  5  should  remain  aloft 
for  a  short  period  to  guard  the  tails  of  machines  1,2, 
and  3,  and  then  join  in  if  i,  2,  and  3  are  not  attacked. 
It  will  be  readily  understood  that,  in  the  case  of  one 
formation  attacking  the  other,  no  rules  of  combat  can 
be  laid  down. 

On  Being  Attacked 

If  you  see  a  hostile  machine  above  you,  try  and 
climb  above  him.     If  this  fails,  try  and  get  into  his 

190 


AERIAL    FIGHTING 

blind  spot  below  the  lower  plane  and  then  turn  and 
try  and  lose  him.  You  can  always  shake  him  off 
by  going  back  to  the  lines  or  joining  a  friendly  for- 
mation. If  you  are  already  in  a  formation  he  will 
probably  not  attack.     If  you  see  that  he  has  got  to 


Jn— ------ 


attack,  steer  a  straight  course  for  the  lines,  imless 
that  course  is  away  from  the  sim,  and  wait  for  him 
to  dive.  It  is  not  advisable  to  turn  and  twist  the 
moment  he  starts  to  dive  or  he  wiU  stop  and  you  will 
have  to  go  through  it  again.  Wait  till  he  is  nearly 
within  decisive  range,  then  put  the  nose  of  your 
machine  down  slightly  and  do  a  turn.  That  is  quite 
sufficient  to  make  him  miss,  and  he  will  probably 
carry  on  his  dive.  Should  you  be  left  at  his  level 
in  a  Sop  with  Scout,  it  is  always  best  to  climb  away. 
If  you  suddenly  hear  a  machine  spin  on  your  tail, 
do  a  side  loop  at  once.  In  all  fighting  in  the  air  keep 
your  head,  put  yourself  in  the  enemy's  position,  and 
do  not  unnecessarily  tackle  any  chance  less  than  an 
even  one. 

The  aviator  who  "bags"  the  most  enemy  machines 

191 


THE  EYES  OF  THE  ARMY  AND  NAVY 

is  the  aviator  who  uses  his  powers  of  observation  and 
fights  with  his  head.  The  others  either  get  killed  or 
get  nerves  in  a  very  short  time,  and  their  respective 
countries  do  not  get  the  full  benefit  of  having  trained 


them.  In  time  of  trouble  it  is  a  very  pleasant  help 
to  put  yourself  in  the  enemy's  place  and  view  the 
situation  from  his  point  of  view.  If  you  feel  fright- 
ened before  an  attack,  just  think  how  frightened  he 
must  be. 

Taking  Aim  in  the  Air 


When  sighting  a  gun  to  fire  at  a  hostile  machine  in 
the  air  the  following  points  have  to  be  considered: 
(i)  The  speed  of  your  own  machine. 

(2)  The  speed  of  the  hostile  machine. 

(3)  The  angle  at  which  your  gun  is  aimed  with 
reference  to  the  path  of  flight. 

192 


AERIAL    FIGHTING 

(4)  The  path  of  flight  of  the  hostile  machine. 

There  are  only  two  cases  in  which  the  target  is  in 
line  with  the  sights  for  effective  fire:  i.  e.,  when  the 
target  is  directly  behind  or  in  front  and  is  at  the 
same  height  relative  to  your  line  of  flight  and  traveling 
along  that  line.  At  all  other  times  the  above  points 
have  to  be  taken  into  account  for  effective  fire.     A 


rough  idea  as  to  the  distance  to  aim  in  front  or  behind 
the  target  is  as  follows: 

(i)  The  speed  of  your  own  machine.  When  aiming 
the  gun  (Lewis  machine-gun)  at  right  angles  to  the 
line  of  flight,  with  your  machine  traveHng  at  the  rate 
of  78  miles  per  hour,  aim  15  yards  in  front  of  the 
target  at  a  range  of  310  yards,  or  30  yards  in  front 

193 


THE  EYES  OF  THE  ARMY  AND  NAVY 

at  a  range  of  620  yards.     This  only  corrects  for  the 
speed  of  your  own  machine. 

(2)  The  speed  of  the  hostile  machine.  If  the  hostile 
machine  is  traveling  at  the  same  speed  as  your  own 
machine  (78  miles  per  hour),  and  in  the  same  direction 


and  parallel  to  your  line  of  flight,  aim  the  15  yards 
in  front  to  allow  for  your  own  speed  and  another  20 
yards  in  front  to  allow  for  the  speed  of  the  hostile 
aircraft,  a  total  of  35  yards  at  a  range  of  310  yards. 
These  corrections  vary  in  direct  proportion  to  the 
range.     (Fig.  43.) 

If  the  target  is  traveling  in  the  opposite  direction, 
aim  5  yards  in  front.     (FHg.  44.) 

194 


AERIAL    FIGHTING 

(3)  The  angle  at  which  your  gun  is  aimed  with  refer- 
ence to  the  path  of  flight.  When  aiming  at  a  machine 
at  an  angle  of  45°,  either  to  the  front  or  rear  of  your 
line  of  flight,  the  correction  for  the  speed  of  your  own 
machine  would  be  9  yards  in  front  or  behind  the 
target,  according  to  its  direction.     To  correct  for  the 


/ 

X 


/     ^ 
/ 


/ 

A 


/\ 


"V 


.\ v^^ — »— I. 


ri«.47 


speed  and  the  direction  of  the  target,  if  it  is  traveUng 
at  right  angles  to  the  barrel  of  your  gun,  aim  20 
yards  in  front,  making  a  total  of  29  yards,  or  11  yards 
in  front,  as  the  case  may  be.     (Figs.  45  and  46.) 

(4)  The  line  of  flight  of  the  hostile  machine.  If  the 
target  is  directly  in  front  or  behind  and  traveling 
along  your  Hne  of  flight,  but  above  it,  with  the  barrel 
of  your  gun  at  about  an  angle  of  45°,  make  the  same 
corrections  as  in  case  (3).     (Figs.  47  and  48.) 

To  make  corrections  for  a  ground  target,  the  speed 
of  the  machine  and  direction   and  velocity  of   the 

19s 


THE  EYES  OF  THE  ARMY  AND  NAVY 

wind  are  the  points  to  be  considered.  To  allow  for  the 
wind  the  target  may  be  considered  to  be  moving  at  the 
same  rate  as  the  wind,  but  in  the  opposite  direction; 
so  in  traveHng  down-wind  aim  in  front  of  the  target, 
and  up-wind  aim  behind  it  for  windage  corrections. 
Aiming  at  a  ground  target  at  an  angle  of  45° — speed 


-11,  ^  10  yanls  ISJ- 


of  the  machine  yS  miles  per  hour,  velocity  of  wind 
20  miles  per  hour,  range  310  yards — aim  15  yards  in 
front  to  allow  for  speed  of  machine,  and  going  down- 
wind allow  5  yards  more  for  the  wind,  making  a 
total  of  20  yards  in  front  of  the  target.  Traveling  up- 
wind it  would  be  necessary  to  aim  only  10  yards  in 
front  of  the  target,  as  the  wind  holds  back  the  missile  5 
yards  instead  of  advancing  it  5  yards.     (Fig.  49.) 

196 


XVII 

LIGHTER   THAN   AIR 

IIGHTER-THAN-AIR  cruisers  are  of  three  types: 
^  The  rigid  is  the  most  efficient  type  and  is 
illustrated  by  the  ZeppeUn.  The  semi-rigid  is  less 
useful,  but  correspondingly  less  expensive.  It  is 
suitable  for  shorter  cruises  and  for  lighter  loads. 
The  French  Lebandy  may  be  taken  as  an  example 
of  this  class.  The  third  type  is  the  non-rigid,  which 
is  the  most  popular,  the  least  costly,  and  the  least 
efficient  class.  To  this  -third  class  belong  the  British 
Blimp,  the  French  Bayard-Clement,  and  the  German 
Parseval.  This  German  product  is  said  to  be  the  first 
representative  of  its  class.  Germany  has  specialized 
in  the  airship  Une  and  leads  the  world  in  this  de- 
partment of  aeronautics. 

The  free  balloon  and  the  captive  balloon  are  also  of 
the  non-rigid  type,  but  these  are  distinct  from  all  other 
aircraft  in  that  they  have  no  means  of  self -propulsion. 
The  free  balloon  is  practically  useless  as  an  instnmient 
of  war,  since  its  movements  cannot  be  controlled  nor 
guided.  The  captive  balloon,  on  the  other  hand,  is  a 
14  197 


THE  EYES  OF  THE  ARMY  AND  NAVY 

very  important  means  of  reconnaissance  over  enemy 
lines. 

The  principal  lighter-than-air  machines  are  the 
German  Zeppelin,  Schutte-Lanz,  Gross,  and  Parseval; 
the  French  Bayard-Clement,  Zodiac,  Astra,  and 
L6bandy;  the  British  Astra-Torres  and  late  Govern- 
ment designs  popularly  known  as  Blimps. 

Hydrogen  and  Coal-gas 

Balloons  and  airship  envelopes  may  be  filled  with 
hydrogen  or  coal-gas.  Hydrogen,  in  a  pure  state,  will 
lift  approximately  70  pounds  per  1,000  cubic  feet; 
although  the  majority  of  balloon  and  airship 
designers  only  allow  for  a  lift  of  67  pounds  per  1,000 
cubic  feet  of  hydrogen.  The  lift  to  be  expected  for 
coal-gas  varies.  According  to  quality  the  lift  varies 
from  41  to  33  pounds  per  1,000  cubic  feet.  This  gas  is 
much  cheaper  than  hydrogen  and  is  easier  to  obtain. 

The  lift  of  both  these  gases  is  subject  to  variation, 
due  to  the  temperature,  himiidity  of  the  atmosphere, 
and  the  height  of  the  barometer. 

Balloons 

The  balloon  envelope  is  usually  constructed  of  var- 
nished silk,  rubber-proofed  silk,  cotton,  or  oiled  silk. 
It  is  spherical  in  shape  and  the  lower  portion  is  usually 

198 


LIGHTER    THAN   AIR 

tapered  off  so  as  to  form  the  neck,  and  at  the  upper 
end  a  circular  opening  is  formed  into  which  a  valve 
seating  is  secured. 

There  are  many  types  of  valves  used  in  the  air 
services,  and  the  majority  are  arranged  to  be  kept 
closed  by  means  of  springs  or  rubber  cords.  These 
valves  are  so  arranged  that  they  are  easily  opened 
by  means  of  the  valve  line.  This  line  is  usually  passed 
through  the  balloon,  out  at  the  neck,  and  thence  into 
the  car. 

The  car  is  generally  constructed  of  basket-work 
and  suspended  from  netting,  which  covers  the  entire 
balloon.  The  upper  part  of  the  netting  terminates  at 
a  circular  grummet  which  slips  around,  and  is  se- 
cured to  the  valve  seating. 

The  majority  of  modem  balloons  and  many  air- 
ships are  fitted  with  a  "ripping  panel,"  the  object 
of  which  is  to  deflate  the  balloon  envelope  quickly. 
This  panel  usually  consists  of  a  strip  of  fabric  sewn 
over  an  opening  in  the  upper  part  of  the  balloon  or 
airship  envelope.  Attached  to  the  upper  portion  of 
this  panel  a  line  is  attached  and  passed  into  the  car  of 
the  aircraft.  The  line  is  invariably  painted  red  and  a 
certain  amount  of  slack  rope  has  always  to  be  gathered 
in  before  the  panel  can  be  thrown  away.  This  device 
acts  as  a  means  of  safety ;  a  small  accidental  piill  will 
not  start  the  "rip." 

199 


THE  EYES  OF  THE  ARMY  AND  NAVY 

The  Equipment  of  a  Balloon 

The  equipment  of  a  balloon  should  consist  of 
anchor,  anchor  rope,  balloon  cloth  for  incasing  gas  bag, 
ballast  (preferably  in  the  form  of  dry  sand),  knife  in 
leather  sheath,  maps  or  charts,  statoscope,  ther- 
mometer, two  aneroid  barometers  (graduated  in 
feet),  trail  ropes,  valve  case,  watch,  and  a  rough  log- 
book and  pencil. 

Doping  and  Varnishing  Envelopes 

Boiled  linseed  varnish  is  a  dope  which  is  used 
considerably  in  the  lighter- than-air  services.  It  is 
important  that  the  varnish  be  of  the  best  quality. 
On  rubber-fabric  envelopes  the  varnish  is  generally 
used  as  a  foundation  on  which  to  apply  aluminium 
paint.  This  kind  of  paint  is  used  to  avoid  the  effect 
of  the  sun  heat.  The  paint  reflects  the  rays  of  the 
sun,  instead  of  allowing  them  to  penetrate  the  en- 
velope and  expand  the  gas. 

Handling  Envelopes 

All  balloon  and  airship  envelopes  should  be  handled 
with  the  greatest  care,  if  their  gas  tightness  is  to  be 
maintained.    For  the  inflation  and  deflation  process, 

200 


LIGHTER    THAN   AIR 

ground  cloths  should  be  spread  out,  and  on  no  account 
should  any  person  wearing  street  boots  or  shoes  be 
allowed  to  walk  on  these  cloths.  Rubber-soled  shoes 
should  be  worn  by  all  men  working  around  airship 
and  balloon  envelopes. 

Storage  of  Envelopes 

Envelopes  should  always  be  stored  in  a  place  free 
from  the  sun's  rays  and  out  of  reach  of  mice  and  rats. 
They  should  never  be  stored  in  a  bmlding  where  they 
may  be  subject  to  extremes  of  weather.  Between  40° 
and  60°  Fahrenheit  is  the  most  favorable  temperature. 
A  rack,  similar  to  a  large  clothes-horse,  has  been 
found  to  be  very  useful  when  folding  and  packing  up 
an  envelope. 

Airship  Planes  and  Rudders 

Movable  planes  are  used  to  alter  the  angle  of  flight 
of  an  airship,  and  fixed  vertical  and  horizontal  planes 
to  stabilize  the  airship  in  flight.  Without  the  hori- 
zontal planes  the  airship  would  be  continually  pitching 
up  and  down,  and  without  the  vertical  fixed  planes  a 
pilot  would  be  unable  to  steer  a  straight  course.  All 
fixed  planes  are  placed  toward  the  aft  end  of  the  air- 
ship and  the  movable  planes  are  usually  attached  to 
the  rear  of  the  horizontal  fixed  planes.    These  planes, 

201 


THE  EYES  OF  THE  ARMY  AND  NAVY 

both  fixed  and  movable,  are  usually  made  up  of  steel 
tubing,  braced  with  wiring  and  king  post,  and  covered 
with  fabric.  The  fabric  is  doped  and  stretched  taut. 
Special  care  should  be  taken  that  the  control  wires 
are  kept  taut  and  well  protected  from  moisture  and 
not  allowed  to  fray. 

Ballonets 

Ballonets  are  internal  balloons  fitted  inside  the  main 
envelope;  arrangements  are  made  in  the  car  of  the 
airship,  so  that  they  can  be  inflated  with  air  from  a 
blower  driven  by  the  engines  or  an  auxiliary  motor. 
For  instance,  an  airship  ascending  from  the  ground 
full  to  i,ooo  feet:  at  the  outset  the  ballonets  are  lying 
empty  at  the  bottom  of  the  envelope,  and  they  re- 
main so  throughout  the  ascent;  by  the  time  the  air- 
ship has  risen  to  i,ooo  feet  it  will  have  lost  ^-  of  its 
volume  of  gas,  which  will  have  escaped  through  the 
valves.  If,  therefore,  the  airship  has  300,000  cubic  feet 
capacity,  it  will  have  lost  10,000  cubic  feet  of  gas. 
The  airship  now  commences  to  descend;  as  it  de- 
scends, the  gas  within  contracts,  and  it  is  necessary  to 
commence  to  blow  air  into  the  ballonets;  by  the  time 
the  craft  reaches  the  ground  10,000  cubic  feet  of  air 
will  have  been  blown  into  the  ballonets  and  the  air- 
ship will  have  retained  its  shape  and  not  be  flabby. 

If  a  second  ascent  is  necessary,  as  the  airship  ascends 

203 


LIGHTER    THAN   AIR 

the  air  must  be  let  out  from  the  ballonets  instead  of 
gas  from  the  envelope;  and,  to  insure  that  this  is 
always  done  the  ballonet  valves  are  set  to  work  at  a 
lower  pressure  than  the  gas  valve;  and  so  by  the 
time  an  altitude  of  1,000  feet  has  been  reached  the 
ballonets  will  be  empty. 

It  will  be  readily  observed  that  in  this  case,  pro- 
vided an  ascent  is  not  made  to  over  1,000  feet,  it  will 
not  be  necessary  to  lose  gas  during  flight. 

Size  of  Ballonets 

The  size  of  ballonets  govern  the  height  to  which  an 
airship  can  ascend;  therefore  the  size  of  them  must 
be  determined  by  the  amount  of  spare  buoyancy  which 
the  aircraft  is  designed  to  possess.  For  instance,  sup- 
pose that  the  volume  of  the  ballonets,  when  fully  in- 
flated, amounts  to  one-quarter  of  the  total  volume,  if 
the  airship  descends  from  7,500  feet,  then  at  sea- 
level  the  ballonets  will  be  loaded  to  capacity;  how- 
ever, if  the  craft  has  risen  to  8,600  feet,  then  on  de- 
scending to  600  feet  the  ballonets  will  be  full,  and  be- 
low this  height  it  would  be  impossible  to  preserve  the 
internal  pressure  or  the  shape  of  the  envelope.  The 
usual  size  of  the  envelope  is,  for  small  airships,  one- 
fifth  of  the  volume;  for  medium-size  airships,  one- 
quarter;    and  for  craft  specially  designed  to  attain 

203 


THE  EYES  OF  THE  ARMY  AND  NAVY 

height,  one-third  of  the  total  volume.  These  sizes 
can  ascend,  roughly,  to  the  maximum  heights  of  6,000, 
7,000,  and  10,000  feet,  respectively;  but  it  should  be 
borne  in  mind  that,  owing  to  the  contraction  of  the 
gas,  when  descending  in  bright  sunlight  or  unfavor- 
able weather,  500  to  1,000  feet  may  easily  be  lost. 

On  active  service  it  frequently  happens  that  an  air- 
ship is  obliged  to  descend  from  a  greater  height  than 
that  which  her  ballonets  can  cope  with,  and  on  such 
occasions  an  extemporized  safeguard  is  fitted. 

Rigging 

The  main  object  of  rigging  is  to  distribute  the  weight 
of  the  car  evenly  over  the  balloon.  Rigging  cables 
are  attached  to  the  car  either  by  eye-bolts  or  toggles. 
At  the  head  of  the  lower  cable  there  is  an  eye  through 
which  runs  the  next  section  of  rigging.  This  method 
enables  the  single  cable  to  be  branched  into  a  double 
cable  and  further  up  the  double  cable  is  again  branched 
off,  each  single  cable  into  a  double  cable,  and  so  on 
until  the  point  of  attachment  is  reached.  The  three 
main  methods  of  attachment  of  the  car  to  the  envelope 
are  by  means  of  the  toggle  flap,  by  a  "goosefoot, " 
or  by  means  of  a  rigging  band. 

The  rigging  is  usually  made  either  of  flexible  steel 
cable  or  hemp  rope.    The  eyes  are  generally  of  alumin- 

204 


LIGHTER    THAN   AIR 

ium,  but  in  the  smaller  type  of  aircraft  they  are  made 
of  boxwood.  All  rigging  is  necessarily  exposed  to  the 
meteorological  elements  and  should  therefore  be  pro- 
tected. 

The  Mooring  of  an  Airship 

Two  methods  of  mooring  an  airship  are  adapted 
in  the  air  services :  by  the  nose  of  the  craft  being  se- 
cured to  a  specially  designed  mooring  mast,  and  by  the 
bridle  to  a  holdfast  in  the  ground.  The  former  of  the 
two  methods  is  the  most  satisfactory  and  is  accom- 
pHshed  by  passing  a  steel  cable  over  a  block  in  the 
cone  of  the  mooring  mast.  One  end  of  the  cable  is 
attached  to  the  nose  of  the  airship  and  the  other  end 
is  shackled  to  a  cable  passing  down  the  center  of  the 
mast  to  a  windlass  at  the  foot  of  the  mast.  The  wind- 
lass is  revolved  and  the  airship  is  hauled  in  until  the 
ngse  of  the  envelope  is  tight  in  the  cone.  The  cone 
should  be  well  padded  to  prevent  injury  to  the 
envelope.  This  operation  should  never  be  attempted 
while  the  car  is  resting  on  the  ground;  it  should  float 
clear  of  the  ground  and  should  be  ballasted  so  that 
the  car  hangs  roughly  horizontal.  When  it  is  desired 
to  release  the  airship  a  trip  catch  is  operated  which 
allows  the  aircraft  to  be  almost  instantly  released. 

The  bridle  method  cannot  be  carried  out  successfully 
unless  the  car  is  equipped  with  swiveling  landing- 

205 


THE  EYES  OF  THE  ARMY  AND  NAVY 

wheels.  The  center  part  of  the  bridle  is  secured  to 
a  holdfast  in  the  ground  and  tightened  up,  until  the 
tail  of  the  craft  points  perceptibly  upward.  The  car 
should  then  be  ballasted  down,  to  prevent  liability  of 
Hfting  in  a  gust. 

Landing  Skids  and  Wheels 

Landing  skids  and  wheels  are  provided  on  air- 
ship cars  to  protect  the  bottom  of  the  car  from  scrap- 
ing along  the  ground  and  thus  damaging  and  strain- 
ing the  craft  in  general.  They  also  protect  the  main 
framework  from  damage  in  a  heavy  landing. 

The  Training  of  an  Airship  Pilot 

Several  balloon  flights  are  a  necessary  preliminary 
training  for  an  airship  pilot.  If  at  any  time  the  power 
plant  of  an  airship  becomes  useless,  an  airship  at 
once  becomes  a  free  balloon,  and  on  such  occasions  a 
knowledge  of  the  effect  of  ballast  and  the  effect  of. 
change  of  temperature  will  be  very  useful.  It  also 
affords  an  excellent  opportunity  for  map-reading 
practice,  the  use  of  the  various  instnmients,  and  in 
making  landings. 

In  the  air  services  the  course  laid  down  for  officers  and 
men  qualifying  as  airship  pilots  includes  four  ascents 

?o(5 


LIGHTER    THAN   AIR 

as  passenger ;  in  the  last  of  these  the  pupil  takes  com- 
plete charge  under  the  supervision  of  an  officer- 
instructor.  Then  one  "solo"  run  of  at  least  an  hour's 
duration  and  one  night  ascent  of  not  less  than  two 
hours'  duration  must  be  taken. 


Piloting  an  Airship 

The  first  fault  found  with  inexperienced  airship 
pilots  is  the  lack  of  maintaining  elevation;  the 
second  fault'  is  that  of  inability  to  maintain  the 
correct  pressure.  There  are  many  ways  to  get  altera- 
tions of  elevation,  and  the  pilot  should  bear  in  mind 
the  relative  value  of  each  and  under  what  circum- 
stances each  should  be  adopted.  The  trimming  planes, 
or  elevators,  are  always  used  to  correct  small  altera- 
tions of  elevation,  but  in  order  to  obtain  a  greater  in- 
clined path  the  filling  of  one  baUonet  with  more 
gas  than  the  others  is  the  best  method.  By  dis- 
tributing the  lift  in  this  way  a  diminution  of  lift  is 
obtained  at  the  point  where  the  fullest  ballonet  is 
situated.  The  result  is  that  there  will  be  an  increase 
of  lift  at  the  opposite  end  and  the  airship  will  tilt 
downward  or  upward  according  to  the  distribution, 
and  will  follow  an  inclined  path  through  the  air. 

Swiveling  propellers  are  sometimes  used,  and  this 
is   the   most   powerful   and   most   direct   method   of 

207 


THE  EYES  OF  THE  ARMY  AND  NAVY 

tilting,  but  it  has  a  great  disadvantage — that  of  im- 
pediment to  the  forward  motion  of  the  craft. 

The  Maintenance  of  Gas  Pressure 

If  the  pressure  in  an  envelope  of  an  airship  becomes 
too  great  there  is  danger  of  the  envelope  bursting,  and 
if  the  pressure  is  allowed  to  become  too  little  the 
craft  may  become  unmanageable;  therefore  it  is 
obvious  that  this  point  is  an  important  one.  If  the 
pressure  falls  too  low  in  an  envelope  of  an  airship, 
the  nose  of  the  craft  is  liable  to  be  blown  in  and  in 
many  cases  the  tail  curls  up.  This  causes  extra  strain 
on  parts  of  the. rigging  and  frequently  the  craft  will 
not  answer  to  the  controls. 

Leaving  the  Ground 

In  piloting  an  airship  having  landing-wheels  or  an 
efficient  skid  gear,  it  is  possible  to  leave  the  ground 
like  an  aeroplane,  providing  the  field  is  large  enough 
and  there  are  no  obstructions.  To  assist  in  a  quick 
rise  the  craft  should  be  ballasted  a  little  light.  The 
forward  ballonet  should  be  light  and  the  aft  ballonet 
heavy.  As  soon  as  the  ship  is  released  by  the  landing 
party  it  will  ascend,  and  will  move  off  at  an  increasing 
angle  as  it  gathers  speed.  In  an  airship  fitted  with 
swiveling  propellers,  the  method  of  leaving  the  ground 

208 


LIGHTER    THAN   AIR 

is  somewhat  different.  The  propellers  are  adjusted 
for  a  direct  lift,  and  if  the  buoyancy  of  the  craft  is 
correct  the  airship  will  rise  almost  vertically.  When 
clear  of  all  obstacles,  forward  motion  by  the  motor 
power  is  maintained. 

In  the  Air 

When  the  airship  rises  the  pressure  will  rise  also, 
and  it  is  usual  to  let  air  out  of  the  aft  ballonet  in  order 
to  adjust  the  trim  of  the  craft.  The  approximate 
loss  of  lift  with  height  is  one-thirtieth  of  the  craft's 
gross  lift  for  every  thousand  feet  rise.  Suppose  a  pilot 
decides  to  fly  at  a  thousand  feet :  When  the  height 
is  attained  the  trimming  planes  are  set  at  the  hori- 
zontal position  and  the  craft  should  fly  on  even 
keel.  However,  if  the  path  of  flight  is  not  maintained 
the  trim  should  be  adjusted  by  blowing  air  into 
whichever  ballonet  is  higher,  and  letting  out  air  in 
the  lower  one.  Rising  currents,  change  of  tempera- 
ture, and  passing  over  water  will  affect  the  elevation  of 
the  craft ;  but  all  slight  corrections  can  be  made  with 
the  trimming  planes. 

Descending 

It  is  important  that  a  descent  be  not  made  so 
rapidly  that  the  blowers  cannot  cope  with  the  de- 

209 


THE  EYES  OF  THE  ARMY  AND  NAVY 

mand  for  air;  therefore  the  speed  of  descent  must  be 
modified  to  suit  the  capacity  of  the  blowers. 


Landing 

The  landing  of  an  airship,  that  is,  to  bring  the  craft 
to  rest,  both  vertically  and  horizontally,  about  fifty 
feet  above  the  landing  party,  is  the  most  difficult  task 
in  the  piloting  of  an  airship.  The  momentum  of  an 
airship  must  be  absorbed  during  the  process  of 
gliding  to  the  landing  party;  this  momentum  is  two- 
fold— ^the  falling  motion  and  the  speed  forward. 
The  former  can  only  be  absorbed  by  the  resistance  of 
the  air  or  by  throwing  out  ballast,  and  the  latter  by 
the  resistance  of  the  air,  although  some  types  of  ships 
are  equipped  with  engines  whose  propellers  can  be 
reversed.  A  pilot  should  ascertain  before  landing  if  a 
craft  is  lighter  than  air  or  heavier  than  air,  and 
exactly  how  much  ballast  will  adjust  it.  Before  the 
craft  is  landed  the  engine  should  be  stopped  or  throt- 
tled down  to  idling  speed.  All  aircraft  should  be 
landed  head  to  wind.  The  trail  rope  should  be 
dropped  when  over  the  landing  party,  and  guy  hands 
below  should  be  in  readiness  to  seize  the  guys  as  soon 
as  they  are  within  reach.  The  landing  party  should 
be  in  front  of  the  craft  and  not  underneath  or  on  one 

2IO 


LIGHTER    THAN   AIR 

side.     The  men  should  haul  in  hand  over  hand  and 
should  stand  their  ground. 

When  landing  craft  that  are  equipped  with  the 
swiveling  propellers,  it  is  possible  to  land  easily, 
although  you  may  be  considerably  lighter  or  heavier 
than  air ;  but,  as  stated  previously,  it  is  necessary  for 
the  pilot  to  know  beforehand  the  buoyancy  of  the 
craft.  If  the  swiveling  propellers  are  tilted  beyond 
45°  up  or  down,  the  steersman  loses  almost  all  control, 
owing  to  the  craft  losing  way.  The  best  method  of 
landing  a  craft  equipped  with  swiveling  propellers  is 
to  descend  to  between  200  and  250  feet  from  the  land- 
ing party  by  use  of  the  planes.  The  swiveling  pro- 
pellers should  then  be  started,  and  if  manipulated 
skilfully  the  craft  can  be  landed  perfectly  without 
discharging  ballast  or  dropping  the  trail  rope.  If  the 
craft  has  a  negative  buoyancy,  very  little  downward 
thrust  will  be  required;  but  a  considerable  upward 
thrust  will  be  required  near  the  ground;  otherwise 
the  craft  will  bump. 

The  qualities  of  a  pilot  are  generally  judged  by  the 
quality  of  landings  which  he  makes.  Sudden  outpour- 
ings of  ballast  at  the  last  moment  indicate  faulty 
judgment.  A  poor  pilot  is  also  indicated  by  dropping 
the  trail  rope  too  soon  or  too  late,  overshooting  or 
undershooting  the  landing  party  and  thus  causing 
the  landing  party  to  have  a  run  for  the  trail  rope. 

211 


THE    EYES   OF   THE   ARMY   AND   NAVY 

Loss  of  Buoyancy 

Loss  of  buoyancy  may  be  due  to :  rise  of  tempera- 
ture, snow,  rain,  falling  of  barometer,  and  loss  of  gas, 
caused  by  continuing  to  rise  after  the  ballonets  are 
empty. 

Gain  of  Buoyancy 

Gain  of  buoyancy  may  be  due  to:  discharge  of 
ballast,  fall  of  temperature,  rise  of  barometer,  petrol 
and  oil  consumption  and  therefore  less  loading;  fre- 
quently an  increase  in  buoyancy  will  be  experienced 
when  a  wet  envelope  is  drying. 


XVIII 

MEDICAL  SUPERVISION   OF   AVIATORS 

AS  the  height  at  which  aviators  carry  out  their 
ii.  respective  duties  and  the  speed  of  aircraft  in- 
crease almost  daily,  a  course  of  medical  training  for 
aviators  has  been  universally  adopted.  Fitness  is 
tested  more  thoroughly  after  the  pupil  has  made  his 
first  few  "solo"  flights,  and  an  invaluable  insight  into 
his  temperament  under  stress  is  given  in  this  way. 

Experience  alone  can  teach  that  a  man  is  fit  to  fly, 
and  medical  men  must  watch  the  results  throughout 
with  sympathy  and  understanding  and  also  with  logic 
and  a  close,  detective  instinct. 

To  fly,  a  man  must  be  temperamentally  and 
physically  fit;  although  this  is  obvious,  it  remains 
somewhat  difficult  to  discover  the  flaws  of  tempera- 
ment likely  to  unfit  the  pupil  for  his  work,  as  some 
of  the  flaws  are  so  fine  that  no  medical  test  can 
reveal  them.  The  would-be  aviator  is  advised  to 
avoid  any  concealment  under  the  mistaken  notion 
that  he  might  be  doing  himself  an  injustice  if  he  tells 

15  213 


THE  EYES  OF  THE  ARMY  AND  NAVY 

the  whole  truth.  If  a  pupil  feels  unfit,  either  tem- 
peramentally or  physically,  he  should  inform  the  prop- 
er authorities.  It  sometimes  happens  that  pupils 
remain  silent  and  do  not  confess  a  disinclination  to 
fly,  fearing  that  the  surgeon  or  instructor  or  their 
brother  pupils  will  saddle  them  with  the  odium  of 
having  "cold  feet." 

An  aviator's  disinclination  to  fly  must  have  its 
basis  upon  some  temporary  defect  of  mind  or  body; 
such  defects  are  often  curable  by  proper  treatment. 
Pupils  should  not  be  unduly  timid  or  sensitive  in 
confessing  their  fears;  therefore  a  candid  confession 
should  be  made  rather  than  tempt  Providence  by 
running  the  risk  of  overtaxing  their  powers.  It  is  a 
mistaken  idea  that  flying  is  wholly  a  question  of 
nerves.  Some  of  the  most  nervous  of  civilians  have 
turned  out  "stunt"  airmen.  Flying  is  a  question  of 
an  active,  well-balanced  mind,  prompt  decision,  and 
a  series  of  sound  and  quick  reflex  actions;  these  are 
defined  as  the  response  to  external  sensations.  An 
aviator  observes  that  the  right  wing  of  his  machine 
is  tilted  up;  the  impression  is  transmitted  through 
the  eyes  to  the  brain,  where  it  is  recorded  and  a  de- 
cision is  made,  which  is  transmitted  to  the  muscles  of 
the  hands,  and  the  control  lever  is  pushed  over  to  the 
right. 

These  impressions  and  actions  constitute  what  is 

214 


MEDICAL    SUPERVISION 

known  in  the  medical  realm  as  the  visual  reflex. 
Twenty-hundredths  of  a  second  is  the  normal  time 
of  the  circuit.  This  visual  reflex  is  the  most  im- 
portant. To  this  accurate  sense  of  sight  and  reflex  the 
best  aviators  owe  their  greatest  feats  and  success. 
The  sense  of  sight  is  essential.  The  other  senses, 
hearing,  touch,  muscular,  and  the  sense  of  equilibra- 
tion and  their  reflexes,  must  be  normal. 

The  rush  of  cold  air  during  flight  often  causes 
temporary  deafness,  and  an  unsuspected  defect  of 
this  kind  may  be  fatal  to  a  beginner.  While  flying 
the  perception  of  such  a  thing  as  diminished  acute- 
ness  of  hearing  is  a  difficult  matter.  An  instructor 
should  test  his  pupil's  hearing  often,  and  occasionally 
while  flying. 

The  cultivation  of  the  sense  of  touch  and  the 
muscular  sense  should  come  in  the  third  and  fourth 
places  in  the  medical  training.  A  man  must  feel 
very  quickly  when  his  machine  bumps,  and  cultiva- 
tion of  these  senses  will  enable  him  to  keep  his  ma- 
chine from  tossing  or  rolling  too  much  in  a  heavy 
wind. 

Anent  the  equilibration  reflex:  It  has  been  proved 
that  a  man  who  smokes  too  much  doesn't  balance  as 
quickly  as  a  non-smoker,  and  an  excess  of  intoxicants 
has  a  bad  effect  on  co-ordination  of  nerves  and  muscles. 
An  aviator  should  have  plenty  of  sleep ;  at  least  eight 

2IS 


THE  EYES  OF  THE  ARMY  AND  NAVY 

out  of  every  twenty-four  hours.  Airmen  should  avoid 
flying  when  hungry.  Vertigo  and  dizziness  in  the 
air  are  caused  by  hunger  or  by  bad  or  indigestible 
food.     Nutritious  and  not  rich  food  is  essential. 

Goggles,  made  of  non-splintering  glass,  should  al- 
ways be  worn  when  flying.  Large  leather  gloves, 
lined  with  wool,  are  recommended.  Tight-fitting 
gloves  should  be  avoided.  Boots  should  be  of  leather, 
lined  with  lamb's  wool;  rubber  boots  are  harmful. 

The  possibilities  of  heat  and  frost-bite  are  practi- 
cally eliminated  if  the  hands  and  face  are  smeared 
with  vaseline.  There  are  two  forms  of  air-sickness; 
one  similar  to  seasickness,  and  the  other  fatigue  and 
sometimes  torpor,  due  to  height  effects.  The  former 
is  sometimes  seen  in  amateurs  who  are  invited  to 
fly  with  experienced  pilots.  Symptoms  of  the  latter 
begin  to  appear  at  an  altitude  of  10,000  feet.  The 
pulse  and  breathing  become  quicker  and  fatigue  and, 
in  some  cases,  torpor  occur.  Experience  does  much  to 
overcome  these  air  effects. 

The  best  type  of  aviator  is  much  of  a  piece  with 
other  good  fighting  men,  but  requires  a  special  train- 
ing under  medical  supervision. 


APPENDIX 


APPENDIX 

DEFINITIONS  AND   METRIC   SYSTEM 

Aerofoil.  A  structure,  analogous  to  the  wing  or  tail  of  a 
bird,  designed  to  obtain  a  reaction  from  the  air  at  right  angles  to 
the  direction  of  its  motion. 

Aileron.  An  apparatus  for  maintaining  the  lateral  stability 
of  an  aeroplane. 

Airscrew.    Includes  both  pusher  and  a  tractor  screw. 

Anemometer.  An  instrument  for  ascertaining  the  velocity  of 
the  wind  at  the  earth's  surface. 

Angle  of  Dihedral.    The  angle  between  two  wings. 

Angle  of  Incidence.  The  angle  a  wing  makes  with  the  direc- 
tion of  motion  relative  to  the  air.  This  angle  is  usually  measured 
between  the  chord  of  the  wind  and  the  direction  of  motion. 

Backing.  Wing  is  said  to  be  "backing"  when  changing 
direction  in  an  anti-cloclcwise  direction. 

Balancing  Flaps.  Aerofoils  used  for  balancing  an  aeroplane 
on  its  longitudinal  axis. 

Ballonet.  Adopted  from  the  French  word  meaning  "a  small 
balloon."  An  envelope  of  an  airship  generally  contains  several 
ballonets. 

Banking.  A  machine  is  said  to  bank  when  one  wing  is  lowered 
and  the  opposite  wing  is  raised,  as  in  the  case  when  a  machine  is 
turning. 

219 


THE  EYES  OF  THE  ARMY  AND  NAVY 

Barograph.  A  recording  barometer,  the  charts  of  which  can 
be  caUbrated  for  showing  either  atmospheric  pressure  or  a  rough 
estimation  of  the  height. 

Barometer.  An  instrument  for  ascertaining  the  pressure  of 
the  atmosphere. 

Basin.  A  small  area  of  level  ground  surrounded  or  nearly 
surrounded  by  hills,  and  also  to  describe  a  district  drained  by  a 
river  and  its  tributaries. 

Blower.  A  fan  of  the  rotary  type,  used  for  blowing  air  into 
balloons  or  ballonets,  and  by  doing  so  maintaining  the  pressure 
in  non-rigid  airships. 

Body.  That  part  of  the  aeroplane  containing  the  engine  and 
passenger,  and  to  which  the  wings  are  attached. 

Bridle.  A  loop  of  rope  attached  at  each  end  to  the  sides  of  the 
envelope  of  an  airship. 

Cabane.  a  French  word  denoting  the  mast  structure  pro- 
jecting above  the  body,  to  which  the  top  load  wires  of  a  mono- 
plane are  attached. 

Caere.    Tail-down. 

Camber  (of  a  wing  section).     The  convexity  of  a  wing  section. 

Cant,  To.    To  tilt. 

Carriage.  That  part  of  the  aircraft  beneath  the  body,  in- 
tended for  its  support  on  land  or  water. 

Chassis.    See  Carriage. 

Chord.  The  straight  line  touching  the  under  surface  of  an 
aerofoil  near  the  leading  and  trailing  edges. 

Conduction  is  the  transference  of  heat  by  contact. 

Contour.  An  imaginary  line  along  the  surface  of  the  ground 
at  the  same  height  above  mean  sea-level  throughout  its  length. 

Control  Lever.  A  lever  by  means  of  which  pitching  and 
rolling  of  the  aeroplane  are  controlled. 

220 


APPENDIX 

Convection  in  a  fluid  is  the  transference  of  heat  by  motion. 

Crest.    The  top  of  a  hill  or  mountain. 

Diffusion.  The  tendency  of  two  different  gases  to  mix  when 
separated  by  a  porous  partition. 

Doping.  Doping  fabric  is  to  paint  it  with  a  fluid,  usually 
containing  a  varnish  of  cellulose  base,  which  tends  to  tighten  and 
protect  the  material.  The  fabric  of  balloons  and  airships  is  also 
doped. 

Drag.    Head  resistance  or  drift. 

Drift.  A  machine  is  said  to  drift  when  it  is  carried  out  of  its 
course  by  a  current  of  air. 

Drift  Bracing.  The  system  of  bracing  used  to  transfer  the 
drag  or  head  resistance  of  the  wings  to  the  body  of  an  aeroplane. 

Drip  Flap.  A  flap  of  fabric  stitched  the  whole  way  rotmd  an 
airship,  or  balloon  envelope,  to  deflect  the  rain  and  prevent  it 
falling  into  the  car. 

Dune.    A  hill  or  ridge  of  sand  formed  by  the  wind. 

Elevator.  An  aerofoil  set  in  a  more  or  less  horizontal  plane, 
used  for  controlling  the  angle  of  incidence. 

Escarpment.    An  extended  line  of  cliffs  or  bluffs. 

Eye.  a  small  ring,  usually  of  boxwood  or  aluminium,  having 
an  annular  groove  on  its  outer  edge,  round  which  a  rope  can  be 
spliced. 

Fairing.  A  piece  added  to  any  structure  to  reduce  its  head 
resistance. 

Fins.  Thin  and  flat  or  slightly  curved  organs,  attached 
parallel  to  the  normal  direction  of  motion  of  an  aircraft.  In  an 
aeroplane  or  seaplane  they  are  always  set  vertically. 

Fuselage.    The  body  of  a  tractor  aeroplane. 

Gap.  The  distance  between  the  upper  and  lower  planes  of  a 
biplane. 

221 


THE  EYES  OF  THE  ARMY  AND  NAVY 

Gliding  Angle.  The  angle,  relative  to  a  horizontal  line  in 
the  air,  at  which  a  machine  descends  with  the  engine  cut  off. 

GoosEFOOT.  Method  of  attaching  the  rigging  on  to  the  en- 
velope of  an  airship. 

Gorge,    A  rugged  and  deep  ravine. 

Hachures.  Hachuring  of  a  vertical  nature  is  the  conventional 
method  of  representing  hill  features  by  shading,  in  short  dis- 
connected lines.  These  lines  are  drawn  in  the  direction  of  the 
flow  of  water  on  the  slopes. 

Handling  Rope.  A  rope  hanging  from  the  envelope  of  an 
airship  and  used  when  manoeuvering  it  on  the  ground. 

Inclinometer.  An  instnunent  for  measuring  the  angle  or 
slope  of  an  aircraft  away  from  the  horizontal. 

Knoll.    A  low  detached  hill. 

Leading  Edge.    The  forward  edge  of  a  plane. 

Leak  Detector.  An  instrument  which  is  used  for  the  purpose 
of  detecting  the  presence  of  hydrogen  and  other  light  gases  in 
the  air.  This  instrument  can  also  be  adapted  to  find  leaks  in  an 
envelope  when  inflated  with  gas. 

Lee,  Leeway,  or  Leeward.  Away  from  the  direction  of  the 
wind.    The  lateral  drift  of  an  aeroplane  to  leeward. 

Lift.  In  aircraft  the  upward  force  in  the  direction  perpen- 
dicular to  the  direction  of  motion  relative  to  the  air.  "Net  lift" 
is  a  term  frequently  applied  to  an  airship,  and  denotes  the  lifting 
capacity  m  fuel,  crew,  and  ballast.  "Gross  lift"  is  used  to  denote 
the  gross  deplacement  of  an  airship. 

Loading.  The  weight  carried  per  vmit  area  of  sustaining  sur- 
face. 

Longeron.    See  Longitudinal. 

Longitudinals.    The  long  fore-and-aft  spars. 

Magnetic  Meridian.    A  magnetic  north-and-south  line. 

222 


APPENDIX 

Meridian  or  North  Line.    A  true  north-and-south  line. 

MooRiNG-CAP.  A  cap,  usually  made  of  fabric,  on  the  nose  of 
an  airship  and  used  to  prevent  rubbing  between  the  envelope 
and  the  cone  of  the  mooring-mast. 

MooRiNG-MAST.  A  mast,  usually  of  steel,  having  a  cone 
mounted  on  the  universal  joint  at  its  top. 

MooRiNG-ROPE.    A  cable  used  for  attaching  an  airship  to  a 

mooring-mast. 

Pancake,  To.  To  drop  like  a  parachute,  with  wings  at  a  very 
large  angle  of  incidence. 

Pass.  A  track  over  a  mountain  range.  Usually  a  depression 
in  the  range. 

Pitch.  The  distance  forward  that  a  screw  propeller  would 
travel  in  one  revolution,  plus  the  slip  of  the  propeller. 

PiTOT  Tube.  A  tube  with  open  end  exposed  to  the  direction 
of  an  aeroplane,  and  which  forms  part  of  the  speed  indicator. 

Plateau.    An  elevated  plain. 

Plotting.  The  process  of  taking  notes  and  sketches  of  ob- 
servations and  measurements. 

Propeller.    An  airscrew  in  a  pusher  machine. 

Pusher.  A  type  of  aircraft  with  the  propeller  behind  the 
wings. 

Pylon.    A  mast  or  post. 

Radiation  is  the  transference  of  heat  by  ether  waves. 

Rib,  Compression.  A  rib  designed  to  act  as  a  strut  between 
the  front  and  rear  spars  of  a  wing. 

Ripping  Panel.  A  strip  of  fabric  on  the  envelope  of  a  balloon 
or  airship  especially  arranged  so  that  it  can  be  torn  away  by  means 
of  a  rope  and  thus  allow  the  gas  to  escape  rapidly. 

Roll,  To.    To  turn  about  the  fore-and-aft  axis. 

223 


THE  EYES  OF  THE  ARMY  AND  NAVY 

Rudder.  A  subsidiary  aerofoil  by  means  of  which  an  aircraft 
is  turned  to  right  or  left. 

Rudder-bar.  The  foot-bar,  by  means  of  which  the  rudder  of 
an  aeroplane  is  worked. 

Salient  or  Spur.  A  projection  from  the  side  of  a  hill  or 
mountain  running  out  of  the  main  feature. 

Setting  or  Orienting.  A  person  is  said  to  set  a  map  when 
placing  a  map  or  plan  so  that  the  north-and-south  line  points 
north  and  south. 

Side  Drift.    See  Drift. 

Side  Slip.  When  a  machine  slips  from  the  path  of  flight, 
either  inward  or  outward,  it  is  said  to  sideslip. 

Skid.  The  part  of  the  landing  gear  of  an  aircraft  designed  to 
support  the  tail  of  the  machine. 

Slip.  The  difference  between  the  actual  progress  of  a  pro- 
peller in  one  revolution  and  its  pitch. 

Span.    The  distance  from  wing-tip  to  wing-tip. 

Spar.  A  long  piece  of  timber  or  beam  which  runs  transversely 
to  the  aircraft. 

Stability,  Directional.  Exists  when  the  aeroplane  tends  to 
travel  along  its  fore-and-aft  axis. 

Stability,  Lateral.  Exists  when  the  tranverse  axis  of  the 
aeroplane  tends  to  return  to  the  horizontal. 

Stability,  Longitudinal.  Exists  when  the  longitudinal  axis 
of  the  aeroplane  tends  to  return  to  the  horizontal. 

Stability,  Natural.  Exists  when  the  aeroplane  tends  to 
return  to  its  normal  attitude  of  flight  and  when  oscillations  about 
that  position  tend  to  decrease  without  the  application  of  the 
controls.    Sometimes  described  as  inherent  stability. 

Stabilizing  Planes.    Planes  fixed  vertically  and  horizontally  on 

224 


APPENDIX 

the  aft  end  of  an  airship's  envelope  to  prevent  pitching  and  to 
aid  in  maintaining  a  course. 

Stagger.  The  wings  of  a  biplane  are  said  to  be  staggered 
wjien  the  wings  are  set  with  the  upper  plane  slightly  ahead  of, 
or  in  rear  of,  the  lower  plane.  The  stagger  is  generally  measured 
by  the  angle  made  with  the  normal  vertical  by  a  line  joining  the 
leading  edges. 

Statoscope.  An  instrument  to  detect  a  small  rate  of  ascent 
or  descent. 

Streamline.  This  term  is  used  when  a  machine  is  so  con- 
structed that  there  is  an  absence,  or  minimum  amount,  of  eddy 
motion. 

Tail.    The  after  part  of  an  aircraft. 

Thimble.  A  metal  "eye"  with  a  grooved  outer  surface  roimd 
which  a  cable  or  rope  is  spliced. 

Tie.    a  structural  member  intended  to  resist  tension. 

Toggle  Flap.  A  toggle  flap  is  a  piece  of  material  sewn  to  the 
envelope  of  an  airship. 

Torque  of  Propeller.  The  tendency  of  a  propeller  to  turn 
an  aircraft  about  its  longitudinal  axis  in  a  direction  opposite  to 
that  in  which  the  propeller  or  tractor  is  revolving. 

Tractor.  The  type  of  aeroplane  with  propeller  in  front  of 
the  wings. 

Trailing  Edge.    The  after  edge. 

Trail-rope.  A  rope  carried  in  an  airship  or  balloon  and 
thrown  out  when  about  to  land  to  enable  the  aircraft  to  be  pulled 
to  the  ground. 

Trajectory  Bands.  A  device  used  in  some  types  of  airships 
for  distributing  the  weight  of  the  car  evenly  over  the  envelope. 

TuRNBUCKLE.     A  form  of  wire-tightener. 

Under-carriage.     See  Carriage. 

225 


THE  EYES  OF  THE  ARMY  AND  NAVY 

Underfeature.  a  minor  feature;  an  offspring  of  a  main 
feature. 

Undulating  Ground.  Ground  which  alternately  rises  and 
falls  gradually. 

Veer,  of  the  Wind.    To  change  direction  clockwise. 

Velocity  of  Sideslip.  The  speed  with  which  the  craft 
moves  broadside  with  respect  to  the  air.   Distinguish  from ' '  Drift. ' ' 

Warp,  To.  To  bend  a  wing  so  that  the  outer  end  of  the  back 
spar  moves  up  or  down.  It  is  convenient  to  call  the  warp  positive 
when  the  movement  is  downward. 

Watercourse,  The  line  defining  the  course  of  water.  The 
lowest  part  of  a  valley,  whether  occupied  by  water  or  not. 

Watershed.  A  ridge  of  land  separating  two  drainage  basins. 
A  summit  of  land  from  which  water  divides  or  flows  in  two  direc- 
tions. This  term  does  not  necessarily  include  the  highest  point 
of  a  range  of  mountains  or  hills. 

Wing  Flaps.    See  Balancing  Flaps. 

Wings.  The  main  supporting  organs  of  an  aeroplane.  A 
monoplane  has  two  and  a  biplane  four. 

Wires,  Drag.  Wires  the  principal  function  of  which  is  to 
transfer  the  drag  of  the  wings  to  the  body  or  other  part  of  the 
aeroplane  structure.  Wires  intended  mainly  to  resist  forces  in 
the  opposite  direction  are  called  "anti-drag  wires." 

Wires,  Lift.  Wires  the  principal  function  of  which  is  to 
transfer  the  lift  of  the  wings  to  the  body  of  the  aeroplane. 

Wires,  Top  Load.  Wires  intended  mainly  to  resist  forces  in 
the  opposite  direction  of  the  lift. 

Wires,  Warp.  Lift  wires  connected  to  the  back  spar  and 
controlled  so  as  to  move  its  outer  end  down  in  warping  the  wing. 

Yaw,  To.  An  aircraft  is  said  to  yaw  when  its  fore-and-aft 
axis  turns  to  the  right  or  left  down  the  line  of  flight. 

226 


APPENDIX 


Metric  Sysieiit 


lo  mm. 
loo  cm. 
i,ooo  m. 
i,ooo  grms. 
i,ooo  kg. 


I  m. 

I  km. 

I  kg. 

I  metric  ton 

I  cm^.  of  water  weighs  i  grm, 

1,000  cm^.  water  =  i  litre  and  weighs  i  kg 


Conversion  Tables 


British 


Metric 


I  in. 

=  25.4  mm. 

I  mm. 

=■  .04  in. 

I  ft. 

=  .3  metre 

I  cm. 

=  .39  in. 

I  yd. 

=  .9  metre 

I  m. 

=  3-3  ft. 

I  mile 

=  1.6  kiloms. 

I  km. 

=  .62  mile. 

I  sq.  in. 

I  sq.  ft. 
I  sq.  yd. 


6.45  cm^ 
.093  m^. 
.84  m^. 


Squared 


I  mm" 
I  cm^. 
I  m^. 


.0015  sq.  m, 
.15  sq.  in. 
10.76  sq.  ft. 


I  cu. in. 
I  cu.  ft. 


16.4  cm^ 
.028  m*. 


Cubed 


I  cm°, 
I  m^. 


.06  cu.  in. 
35.3  cu.  ft. 


THE   END 


24093 


Hrrr 


UC  SOUTHERN  REGIONAL  LIBRARY  FACILITY 


A     000  674  359     5 


